Smog monitor

ABSTRACT

PCT No. PCT/AU89/00367 Sec. 371 Date Apr. 8, 1991 Sec. 102(e) Date Apr. 8, 1991 PCT Filed Aug. 30, 1989 PCT Pub. No. WO90/02329 PCT Pub. Date Aug. 3, 1990.The amount of smog formed in air and the smog concentration in air is determined by measuring the consumption of nitric oxide.

TECHNICAL FIELD

This invention relates to methods and systems for analysing theformation of smog in air, and more particularly for determining:

(a) rate coefficient of smog formation in air;

(b) rate of smog formation in air under selected temperature andillumination conditions;

(c) time required for maximum smog formation in air under selectedtemperature and illumination conditions;

(d) time period during which smog formation in air has occurred;

(e) location of a source of Reactive Organic Compounds (ROC) present inair;

(f) time required for production of a given amount of smog in air;

(g) concentration of smog in air;

(h) amount of prior smog formation in air;

(i) maximum potential smog formation in air;

(j) current extent of smog formation in air;

(k) ozone concentration in air;

(l) nitric oxide, NO and/or ozone concentrations in air;

(m) Reactive Organic Compounds (ROC) concentration of air; and/or

(n) total concentration of ROC previously introduced into air. Thefollowing parameters can also be determined from the methods and systemsof the invention: total concentration of nitric oxide previouslyintroduced into air, total concentrations of NO_(x) and NO_(y)previously introduced into air, ROC/NO_(x) concentration ratio of thetotal ROC and NO_(x) previously introduced into air and average time ofprior introductions of ROC into air.

BACKGROUND ART

Photochemical smog, which is commonly characterized by ozoneconcentrations in the order of 0.1 ppm or greater in air, is an airquality problem in many urban areas, particularly those with high levelsof sunlight.

Photochemical smog formation passes through three sequential phases: (1)oxidation of NO to NO₂, (2) production of O₃, and (3) a final phase whenO₃ is maintained at, or near, its maximum amount. Chemical processesoccurring during each phase are intimately related and interactionsbetween various competing and consecutive chemical reactions makeanalysis of smog formation difficult. Also because the atmosphere in astate of dynamic flux since, as well as changing dispersion variables,there are changing emissions and changing meteorological conditions,e.g. sunlight, rain and temperature. In the atmosphere smog formationdoes not always reach completion because reactants are often dispersedbefore the final phase.

As a consequence of the above difficulties there is presently, despiteconsiderable prior research efforts, a need for systems and methodswhich can provide reliable measures of smog formation in the atmosphere.

The commonly employed measure of smog concentration, ozoneconcentration, gives only a partial indication of the amount of smogformation. This problem arises because many chemical species, inaddition to ozone, are products of the smog forming reactions and alsobecause ozone is not a stable compound and is readily consumed,especially by reaction with nitric oxide. Thus at any given time theobserved concentration of ozone in air is dependent upon the amount ofprior emissions of nitric oxide into the air.

Considerable efforts by the inventor have thus been directed towardsdeveloping a robust method for determining the amount of photochemicalsmog formation in air and a laboratory size smog chamber which providesreproducible and accurate estimates of the photochemical reactivtypotential of air being tested therein. However, it has been found thatprior art smog chambers are prone to give irreproducible and inaccurateresults which are thought to be due to different contributions from manyvariables, e.g. nature of the chamber walls and surface reactionstherewith, shaded zones in the chamber, mixing rates, outgassing,chamber pretreatment, chamber deposits, impurities in reactants,non-uniform temperatures, etc. and smog reaction rates that aredependent on the extent of reaction.

There is also a need for a method for predicting smog formation fromReactive Organic Compounds (ROC)/air mixtures. Such a method could beused for screening solvents and fuels and assessing thephotoreactivities of hydrocarbon wastes.

Photochemical smog formation from reactive organic compounds(ROC)/nitric oxide/air mixtures occurs as follows: ##STR1##

Present methods for measuring the essential reactant, ROC, which isessential for smog formation in the atmosphere are inadequate since theyare either not sufficiently sensitive, are very cumbersome andlabour-intensive or do not take account of the widely differing smogforming reactivities of the individual organic species which takentogether comprise ROC. Frequently, the atmospheric concentrations of theindividual ROC species, while sufficient to produce significantquantities of photochemical smog, are too small to be detected by thecurrently available sensors. Air can be analysed for ROC by highresolution gas chromatography using flame ionisation or photoionizationdetectors but these techniques require cumbersome samplepreconcentration procedures, are labour-intensive and give data on onlya subset of the photochemically active species present.

Furthermore, knowledge of the concentrations of the components of theROC mixture does not allow the photochemical reactivity of the air to bequantitatively estimated because the role of many of the individual ROCspecies, and their reaction products, in the chemistry of smogformation, is uncertain. An approach sometimes adopted for ROC analysisis to measure the total non-methanic hydrocarbon concentration of theair as a single peak, backflushed from a chromatographic column aftermethane has been eluted, or alternatively as the difference in signalfrom air and air scrubbed of ROC species but without methane removal.

For some purposes this arrangement provides adequate sensitivity but themethod is subject to errors in the measured concentrations because noaccount can be taken of the differing sensitivities of the detector tothe various individual ROC species.

In other words, these techniques typically do not provide a measure ofthe reactivity of the total ROC in air since they do not provide the ROCcompositions and this is important since in the atmosphere 250 or moreROC species have been identified of which there can be 60 major speciesor more and the rate of smog formation can be greatly affected by thenature and the relative proportions of the ROC species which arepresent.

Photochemical smog formation is a complex process wherein a multitude ofreactant species are simultaneously consumed to give a wide variety ofchemical product species. It is possible to measure the concentrationsof many of these reactants and products and in the past suchmeasurements have been utilized in various ways as indicators of theextent of photochemical smog production. For example, some measures thathave been used to evaluate extent of reaction are: ozone concentration,peroxyacetyl nitrate concentration; nitrogen dioxide concentration; timeto reach a maximum ozone concentration; time taken for theconcentrations of NO and NO₂ to be equal, ozone concentration attainedafter illumination for a fixed period and intensity; time for NOconcentration to reach one half of its initial value. Such data,however, gives only a limited indication of the progress of reaction andare complex and difficult to interpret in terms of the overall rate andextent of the smog-forming reactions. Additionally the rates at whichthese individual reactants and products are consumed and produced varyas smog formation progresses.

OBJECTS OF INVENTION

Objects of this invention are to provide methods and systems foranalysing the formation of smog in air, and more particularly fordetermining:

(a) rate coefficient of smog formation in air;

(b) rate of smog formation in air under selected temperature andillumination conditions;

(c) time required for maximum smog formation in air under selectedtemperature and illumination conditions;

(d) time period during which smog formation in air has occurred;

(e) location of a source of Reactive Organic Compounds (ROC) present inair;

(f) time required for production of a given amount of smog in air;

(g) concentration of smog in air;

(h) amount of prior smog formation in air;

(i) maximum potential smog formation in air;

(j) current extent of smog formation in air;

(k) ozone concentration in air;

(l) nitric oxide, NO_(y) and/or ozone concentrations in air;

(m) ROC concentration of air; and/or

(n) total concentration of prior ROC emissions into air.

    ______________________________________                                        DEFINITIONS                                                                   Air         Atmospheric air, including pristine air and                                   pristine air into which smog-forming sub-                                     stances (including ROC and NO.sub.x have                                      been introduced at some times (including                                      up to some days) previously. Air may                                          have undergone various transport and                                          dispersion processes including mixing                                         with air of other compositions and                                            dilution by pristine air;                                         a.sup.t .sub.ROC                                                                          Activity coefficient for smog formation by ROC at                             time t; (units: moles smog/mole ROC/unit                                      illumination/unit f(T) or moles smog/mole ROC carbon/                         unit illumination/unit f(T))                                      a.sub.ROC(i)                                                                              Activity coefficient for smog formation from species                          ROC(i);                                                           V.sup.t     Volume at time t;                                                 G.sup.t     A parameter determined according to equation (58);                H           Coefficient of expression (70) and formulae derived                           from (70);                                                        L           Coefficient of expression (70) and formulae derived                           from (70);                                                        E.sup.t .sub.smog                                                                         the extent of smog formation in air at time t, extent                         being the proportion of amount of smog produced by                            time t compared to the maximum potential amount of                            smog formation;                                                   NO.sub.x    NO + NO.sub.2 ;                                                   NO.sub.y    "Total gaseous oxidized nitrogen" is the                                      sum of NO,NO.sub.2, peroxynitric acid,                                        (HO.sub.2 NO.sub.2); nitric acid (HNO.sub.3); peroxy-                         acetyl nitrate, (PAN); nitrous acid                                           (HNO.sub.2), dinitrogen pentoxide (N.sub.2 O.sub.5),                          nitrate radical (NO.sub.3 .sup..) and other gaseous                           organic nitrates. Other nitrogen species at                                   lower oxidation states, e.g. N.sub.2 O, N.sub.2,                              NH.sub.3, HCN, CH.sub.3 CN are not                                            components of NO.sub.y ;                                          Smog Concentration                                                                        The sum of the concentrations of ozone and                                    NO.sub.y less the concentration of NO;                            Amount of   The gross amount of nitric oxide oxidized in                      Smog Formation                                                                            the air by smog chemistry, i.e. the                                           moles of NO consumed by the reaction:                                         RO.sub.2 .sup.. + NO → Products;                           RO.sub.2 .sup..                                                                           Hydroxyl, alkoxy and peroxy free radical species;                 ROC             Reactive organic compounds including carbonyl,                ROC'            alkane, alkene, aromatic, carbon monoxide and other           ROC"            types of gasphase carbonaceous species which when             ROC'"           present in illuminated air undergo reaction wherein                           oxygen molecules are consumed and nitric oxide is                             oxidized;                                                     ROC(i)      A specified individual ROC compound or a specified                            mixture of ROC compounds.                                         .sup.T,I.sub.Q t.sbsb.smog                                                                Rate of smog formation in air at time (t) with                                temperature (T) and illumination intensity (I);                   X.sub.smog .sup.t                                                                         The mole fraction of smog in air at time t;                       I.sub.X.sbsb.i                                                                            The mole fraction of species i in the mixture after                           the first selected period;                                        II.sub.X.sbsb.i                                                                           The mole fraction of species i in the mixture after                           the second selected period;                                       III.sub.X.sbsb.i                                                                          The mole fraction of species i in the mixture after                           the third selected period;                                        X.sub.i .sup.t                                                                            The mole fraction of species i in air at time t                               (mole fraction);                                                  n.sub.i .sup.t                                                                            Number of Moles, n, of species i in air of volume                             V.sup.t at time t (moles);                                        .sup.m V.sup.t                                                                            The volume of a defined parcel of air (m) at time t;              .sup.f n.sub.smog .sup.t                                                                  Amount of previous smog formation in air of volume                            V.sup.t at time t (moles);                                        .sup.o n.sub.i                                                                            Denotes emissions of number of moles, n, of species i                         into air;                                                         .sup.o n.sub.i .sup.t                                                                     Cumulative emissions of species i into air of volume                          V.sup.t during time period t = O to t = t, in moles;              n.sub.NO.sbsb.x .sup.t                                                                    n.sub.NO .sup.t + n.sub.NO.sbsb.2; .sup.t                         .sup.o F.sub.NO                                                                           The fraction of NO in NO.sub.x emissions (.sup.o n.sub.NO                     /.sup.o n.sub.NO.sbsb.x);                                         .sup.f X.sub.smog .sup.t                                                                  The notional concentration of smog formed in air in                           the absence of NO.sub.y removal processes (mole                               fraction);                                                        o.sub.X.sbsb.i t                                                                          The cumulative emissions of species i into                                    air expressed as a fraction of the moles of                                   species i emitted to the moles of air (mole                                   fraction);                                                        .sup.extra X.sub.smog .sup.t                                                              Concentration of smog to be produced at                                       some future time (mole fraction);                                 added.sub.n.sbsb.i                                                                        Number of moles, n, of species i added to the air in                          the course of analysis (moles);                                   .sup.I n.sub.NO                                                                           Number of moles, n, of NO present after first                                 selected period (moles);                                          k.sub.j .sup.t                                                                            Rate coefficient of reaction j at time t;                         R.sub.j .sup.t                                                                            Rate of reaction j at time t;                                     P.sub.j,k   Ratio of rate of reaction j to rate of reaction k                             P.sub.j,k = R.sub.j /R.sub.k ;                                    .sup.fmax n.sub.smog                                                                      Maximum potential moles of smog formation in air;                 .sup.Tmax n.sub.smog                                                                      Maximum potential moles of smog that can be present                           in air, being total of contributions from both smog                           formation processes and emissions of NO.sub.2 ;                   .sup.select X.sub.smog                                                                    A selected concentration of smog in air (mole                                 fraction);                                                        .sup.fmax X.sub.smog .sup.t                                                               Maximum potential concentration of smog formed in                             air (mole fraction);                                              .sup.Tmax X.sub.smog .sup.t                                                               Maximum potential concentration of smog that can                              be present in air, being total of contributions                               from both smog formation processes and emissions                              of NO.sub.2 into air (mole fraction);                             R.sub.smog .sup.t                                                                         Rate coefficient for smog formation at time t;                    R           Gas constant;                                                     p.sup.t     Pressure at time t;                                               T.sup.t     Temperature at time t;                                            X.sub.i .sup.r                                                                            Concentration of species i in reference air;                      v.sub.n     Volume injected by device n in a specified time;                  f           Flowrate;                                                         I.sup.t     Illumination intensity (in units of rate                                      coefficient for NO.sub.2 photolysis, min.sup.-1).                 γ     Coefficient of equation (39);                                     β      A coefficient of smog formation.                                  "reference  Can be simply known temperature and                               temperature and                                                                           illumination conditions or can be conditions                      illumination                                                                              determined with reference                                         conditions" to a reference gas under the same or known                                    temperature and illumination conditions.                          ______________________________________                                    

DISCLOSURE OF INVENTION

The present inventor has found that the amount of smog formed in air andthe smog concentration in air can be determined by the consumption of asingle species, namely nitric oxide, and more particularly the oxidationof NO. A key step leading to smog formation is the dissociation ofoxygen molecules by various smog forming reactions. The present inventorhas found that for each oxygen molecule thus dissociated it can be takenthat an approximately equivalent amount of nitric oxide is caused to beconsumed.

Measurement of the total amount of nitric oxide consumed thus provides aquantitative measure of the amount of smog produced. The rate of smogformation can be determined by the amount of smog produced, as indicatedby nitric oxide consumption (and thus oxygen dissociation) in thepresence of excess nitric oxide, during a selected period under selectedconditions of illumination and temperature. Alternatively, for themeasurement of smog formation rate the total amount of nitric oxideconsumed during the selected reaction period can be determined byaddition of excess ozone to the air prior to the selected period inwhich circumstances the gross consumption of nitric oxide is measured asincrease in ozone concentration, there being an equivalence between thenitric oxide consumed and the ozone produced under the selectedconditions. Brief summaries of the techniques used to determine variousparameters are given below:

1A. Determination of the Amount of Smog Formed in Air

This can be achieved by firstly sampling the air, secondly adding NO sothat it is present in excess and, thirdly, measuring the differencebetween the total amount of nitric oxide which has been present in theair (i.e. the NO emissions into the air prior to sampling plus thatadded during analysis) and the concentration of residual NO presentafter the added NO has been allowed to react with and be consumed by anyozone that may have been present in the air.

1B. Determination of Smog Concentration in Air

Concentration of smog in air is determined by addition of excess nitricoxide to the air and after reaction with substantially all ozone presentdetermining the concentration of smog as the difference between thetotal concentration of the oxidised nitrogen species (i.e. NO, NO₂,peroxyacetyl nitrate, gaseous nitric acid etc) in the mixture and thenitric oxide concentration of the mixture.

A second function of the nitric oxide addition is that by removing ozoneit stabilises the air in the dark, minimising the production of nitricacid within the apparatus. This is beneficial because nitric acid isreadily absorbed on surfaces and can thus be lost from the gas phasewithin the apparatus and before being measured at the detector.

2A. Determination of Rate Coefficient for Smog Formation

Rate coefficient for smog formation is determined by subjecting aircontaining excess NO to photochemical reaction under controlledconditions of temperature and illumination and by measuring the rate atwhich excess nitric oxide is consumed. A second function of the additionof excess nitric oxide to the air is that when excess nitric oxide ispresent the rate of nitric oxide consumption is, to a goodapproximation, independent of the extent of smog formation. Addition ofexcess nitric oxide makes the measured rate of smog formationindependent of the original nitric oxide concentration of the air.

A further function of the excess nitric oxide is that it minimises theconcentration of ozone in the system, thus minimising the ozone inducedside reactions such as formation of nitric acid and nitrous acids in theunilluminated parts of the system. Ozone can also undergo unwantedreactions in the dark with alkenes.

2B. Determination of Rate Coefficient for Smog Formation in Air

Rate coefficient for smog formation in air is determined by subjectingair containing excess ozone to photochemical reaction under controlledconditions of temperature and illumination and by measuring the rate atwhich further amounts of ozone are produced. In the presence of excessozone, nitric oxide is consumed by the smog-forming reactions to producenitrogen dioxide. Nitrogen dioxide undergoes photochemical reaction toproduce ozone and regenerate nitric oxide. A small, steady state, nitricoxide concentration is thus maintained. The net amount of ozone producedunder these conditions is a measure of the amount of nitric oxideconsumed by smog formation and is thus a measure of the amount of oxygenmolecules consumed by smog formation.

3. Prediction of Extent of Maximum Potential Smog Formation in Air

Prediction of the extent of maximum potential smog formation in beascertained by determination of rate coefficient of smog formation, smogconcentration and the total oxidised nitrogen concentration of the air(NO_(y)) and the application of computational formulae as describedherein.

4. Prediction of Rate and Extent of Smog Formation in Air Under SelectedConditions

Prediction of the rate and extent of smog formation that would apply tosampled air when subjected to a wide range of selected atmosphericconditions can be ascertained from the above determined properties ofthe air and application of the computational formulae described herein.

5. Determination of Time Required for Formation of Selected Amounts ofSmog in Air Under Selected Conditions

Determination of the time required for formation of selected amounts ofsmog in air under a wide range of selected conditions can be ascertainedfrom the above determined properties of the air and application of thecomputational formulae described herein.

6. Determination

ROC concentration is determined by subjecting air containing excess NOto photochemical reaction under controlled conditions of temperature andillumination for a selected period and by measuring the concentrationexcess nitric oxide consumed. The nitric oxide consumption isproportional to the ROC concentration of the air and is thus a measureof the ROC concentration of the air. A second function of the additionof excess nitric oxide to the air is that when excess nitric oxide ispresent nitric oxide consumption is, to a good approximation,independent of the extent of previous photochemical reaction involvingthe ROC. Addition of excess nitric oxide makes smog formationindependent of the original nitric oxide concentration of the air.

A further function of the excess nitric oxide is that it minimises theconcentration of ozone in the system, thus minimising ozone induced sidereactions such as formation of nitric acid in the unilluminated parts ofthe system. Ozone can also undergo unwanted reactions in the dark withalkenes.

    ______________________________________                                        TABLE SUMMARISING EMBODIMENTS                                                 Number of                                                                     Embodiment                                                                             Brief Description of Embodiments                                     ______________________________________                                         1       Method for determining rate coefficient of smog                               formation in air; (via NO excess);                                    2       Method for determining rate coefficient of smog                               formation in air; (via O.sub.3 excess);                               3       Method for determining concentration of smog in                               air;                                                                  4       Method for determining amount of prior smog                                   formation in air;                                                     5       Method for determining maximum potential and                                  optionally the current extent of smog formation                               in air;                                                               6       Method for determining rate of smog formation in                              air under selected temperature and illumination                               (via excess NO);                                                      7       Method for determining rate of smog formation in                              air under selected temperature and illumination                               (via excess O.sub.3);                                                 8       Method for determining time required for                                      maximum smog formation in air under selected                                  conditions of illumination and temperature;                           9       Method for determining time period during which                               smog formation in air has occurred;                                  10       Method for determining time required for produc-                              tion of a given amount of smog in air under                                   selected temperature and illumination conditions;                    11       Method of determining ozone concentration in air                              (via determined NO and smog concentrations);                         12       Method for determining nitric oxide and NO.sub.y or                           ozone or both concentrations in air (via de-                                  termined sunlight, temperature, NO.sub.y and smog                             concentrations);                                                     13       System for determining rate coefficient of smog                               formation in air (corresponding to method 1,                                  via NO);                                                             14       System for determining rate coefficient of smog                               formation in air (corresponding to method 2, via                              O.sub.3);                                                            15       System for determining concentration of smog in                               air (corresponding to method 3);                                     16       System for determining amount of prior smog                                   formation in air (corresponding to method 4);                        17       System for determining maximum potential and                                  optionally the current extent of smog formation                               in air (Corresponding to method 5);                                  18       System for determining rate of smog formation                                 in air under selected temperature and illumination                            conditions (corresponding to method 6, NO                                     excess);                                                             19       System for determining rate of smog formation in                              air under selected temperature and illumination                               conditions (corresponding to method 7, O.sub.3 excess);              20       System for determining time required for maximum                              smog formation in air under selected conditions of                            illumination and temperature (corresponding to                                method 8);                                                           21       System for determining time period during which                               smog formation in air has occurred (corresponding                             to method 9);                                                        22       System for determining time required for pro-                                 duction of a selected amount of smog in air under                             selected temperature and illumination conditions                              (corresponding to method 10);                                        23       System for determining ozone concentration of air                             (corresponding to method 11, via determined NO                                and smog concentrations);                                            24       System for determining nitric oxide and NO.sub.y or                           ozone or both concentrations in air (corresponding                            to method 12);                                                       25       Method for determining ROC concentration of air                               and/or total concentration of prior ROC emissions                             into air; and                                                        26       System for determining ROC concentration of air                               and/or total concentration of prior ROC emissions                             into air (corresponding to method 25).                               ______________________________________                                    

According to a first embodiment of this invention there is provided amethod for determining rate coefficient of smog formation in air, themethod comprising:

(a) adding excess nitric oxide to the air to provide an excess nitricoxide/air mixture;

(b) permitting the mixture to react for a first selected period whereinexcess nitric oxide in the mixture reacts with substantially all ozonein the mixture;

(c) determining a first nitric oxide concentration of the mixture afterthe first selected period;

(d) illuminating the mixture of (a) or the mixture after the firstselected period for a second selected period under reference temperatureand illumination conditions;

(e) permitting the mixture, after illumination, to react for a thirdselected period wherein excess nitric oxide in the mixture reacts withany ozone present in the mixture;

(f) determining a second nitric oxide concentration of the mixture afterthe third selected period; and

(g) determining the rate coefficient of smog formation from the firstand second nitric oxide concentrations, the reference temperature andillumination conditions and the duration of the second selected period.

According to a second embodiment of this invention there is provided amethod for determining rate coefficient of smog formation in air, themethod comprising:

(a) adding excess ozone to the air to provide an excess ozone/airmixture;

(b) permitting the mixture to react for a first selected period whereinexcess ozone in the mixture reacts with substantially all nitric oxidein the mixture;

(c) determining a first ozone concentration of the mixture after thefirst selected period;

(d) illuminating the mixture of (a) or the mixture after the firstselected period for a second selected period under reference temperatureand illumination conditions;

(e) permitting the mixture, after illumination, to react for a thirdselected period wherein excess ozone in the mixture reacts with anynitric oxide present in the mixture;

(f) determining a second ozone concentration of the mixture after thethird selected period; and

(g) determining the rate coefficient from the first and second ozoneconcentrations, the reference temperature and illumination conditionsand the duration of the second selected period.

Optionally the method of the second embodiment further includes the stepof (a)(i) adding a quantity of nitrogen oxides to the mixture prior tostep (b). This optional step is recommended for those occasions when thenitrogen oxides concentration of the air is small and limiting on therate of reaction during step (d).

According to a third embodiment of this invention there is provided amethod for determining concentration of smog in air, which methodcomprises:

(a) adding excess nitric oxide to the air to provide an excess nitricoxide/air mixture;

(b) reacting the mixture for a selected period wherein the excess nitricoxide reacts with substantially all ozone in the mixture;

(c) determining the nitric oxide concentration of the mixture after theselected period;

(d) determining the total oxidized nitrogen (NO_(y)) concentration ofthe mixture after the selected period; and

(e) determining the concentration of smog in the air from the nitricoxide concentration of (c) and the NO_(y) concentration of (d).

Optionally the method of the third embodiment further includes the stepof (c)(i) converting NO_(y) in the mixture to nitric oxide prior to step(d). When step(c)(i) is included the NO_(y) concentration in step d) canbe determined by simply determining the nitric oxide concentration ofthe mixture.

According to a fourth embodiment of this invention there is provided amethod for determining the amount of prior smog formation in air, whichmethod comprises:

(A) determining NO_(y) concentration of air;

(B) determining the concentration of smog in air by the method of thethird embodiment;

(C) determining the concentration of total nitrogen oxides previouslyemitted into the air from the NO_(y) concentration in the air and theconcentration of smog in the air; and

(D) determining the amount of prior smog formation in air from theconcentration of total nitrogen oxides previously emitted into the airas determined in step (C) and the concentration of smog in the air asdetermined in (B).

Optionally the method of the fourth embodiment further includes thesteps of (A)(i), converting NO_(y) in the air to nitric oxide prior tostep (A). When step (A)(i) is included the concentration in step (A) canbe determined by simply determining the nitric oxide concentration ofthe air.

According to a fifth embodiment of this invention there is provided amethod for determining maximum potential smog formation in air, whichmethod comprises:

(α) determining the amount of prior smog formation in air by the methodof the fourth embodiment;

(β) determining the concentration of total nitrogen oxides previouslyemitted into the air from the NO_(y) concentration in the air and theconcentration of smog in the air; and

(γ) determining the maximum potential smog formation in the air from theconcentration of total nitrogen oxides previously emitted into the air.

According to a sixth embodiment of this invention there is provided amethod for determining rate of smog formation in air under selectedtemperature and illumination conditions, which method comprises:

(a) adding excess nitric oxide to the air to provide an excess nitricoxide/air mixture;

(b) permitting the mixture to react for a first selected period whereinexcess nitric oxide in the mixture reacts with substantially all ozonein the mixture;

(c) determining a first nitric oxide concentration of the mixture afterthe first selected period;

(d) illuminating the mixture of (a) or the mixture after the firstselected period for a second selected period under selected temperatureand illumination conditions;

(e) permitting the mixture, after illumination, to react for a thirdselected period wherein excess nitric oxide in the mixture reacts withany ozone present in the mixture;

(f) determining a second nitric oxide concentration of the mixture afterthe third selected period; and

(g) determining the rate from the First and second nitric oxideconcentrations and the duration of the second selected period.

According to a seventh embodiment of this invention there is provided amethod for determining rate of smog formation in air under selectedtemperature and illumination conditions, which method comprises:

(a) adding excess ozone to the air to provide an excess ozone/airmixture;

(b) permitting the mixture to react for a first selected period whereinexcess ozone in the mixture reacts with substantially all nitric oxidein the mixture;

(c) determining a first ozone concentration of the mixture after thefirst selected period;

(d) illuminating the mixture of (a) or the mixture after the firstselected period for a second selected period under selected temperatureand illumination conditions;

(e) permitting the mixture, after illumination, to react for a thirdselected period wherein excess ozone in the mixture reacts with anynitric oxide present in the mixture;

(f) determining a second ozone concentration of the mixture after thethird selected period; and

(g) determining the rate from the first and second ozone concentrationsand the duration of the second selected period.

Optionally the method of the seventh embodiment further includes thestep of (a)(i) adding a quantity of nitrogen oxides to the mixture priorto step (b). This optional step is recommended for those occasions whenthe nitrogen oxides concentration of the air is small and limiting onthe rate of reaction during step (d).

According to an eighth embodiment of this invention there is provided amethod for determining time required for maximum smog formation in airunder selected conditions of illumination and temperature, the methodcomprising:

(A) determining rate coefficient of smog formation in the air accordingto the method of the first or second embodiments or;

(A)(i) determining rate of smog formation in the air under the selectedconditions according to the method of the sixth or seventh embodiments;

(B) determining maximum potential smog formation in the air according tothe method of the fifth embodiment; and

(C) determining the time for maximum smog formation, under selectedtemperature and illumination conditions, From the maximum potential smogformation and the rate coefficient; or

(C)(i) determining the time for maximum smog formation, under selectedtemperature and illumination conditions, from the maximum potential smogformation and the rate.

According to a ninth embodiment of this invention there is provided amethod for determining time period during which smog formation in airhas occurred, the time period being substantially the same as or withinpredetermined period for which the illumination and temperatureconditions are known, wherein the end of the predetermined periodcoincides with the end of the time period, the method comprising:

(A) determining temperatures of the air for the predetermined period;

(B) determining sunlight intensities for the predetermined period;

(C) determining the rate coefficient of smog formation according to themethod of the first or second embodiments; or

(C)(i) determining rates of smog formation in the air according to themethods of the sixth or seventh embodiments under temperatures and lightintensities corresponding to the determined temperatures and sunlightintensities;

(D) determining the amount of prior smog formation in the air at the endof the time period according to the method of the fourth embodiment; and

(E) determining the time period during which the smog formation in theair has occurred from the amount of prior smog formation, the ratecoefficient, the determined temperatures and sunlight intensities, or

(E)(i) determining the time period during which the smog formation inthe air has occurred from the amount of prior smog formation and therates of smog formation.

Optionally the location of the source of ROC present in air may bedetermined on the basis of the time period of smog formation andseparately determined speed of movement and trajectory of the air duringthe time period.

According to a tenth embodiment of this invention there is provided amethod for determining time required for production of a selected amountof smog in air under selected temperature and illumination conditionsand with selected initial amount of smog in the air, the methodcomprising:

(A) determining rate coefficient of smog formation in air according tothe method of the first or second embodiments; or

(A)(i) determining rates of smog formation in the air under the selectedtemperature and illumination conditions according to the method of thesixth or seventh embodiments;

(B) determining NO_(y) concentration of the

(C) determining the amount of NO_(y) previously emitted into the airfrom the NO_(y) concentration of (B) and the selected initial amount ofsmog in the air; and

(D) determining the time required for production of selected amount ofsmog in the air for the selected conditions of temperature andillumination from the rate coefficient and the amount of NO_(y) ; or

(D)(i) determining the time required for production of the selectedamount of smog in the air for the selected conditions of temperature andillumination from the rate and the amount of NO_(y) previously emittedinto the air.

Optionally the method of the tenth embodiment further includes the stepsof(A)(i), converting NO_(y) in the air to nitric oxide prior to step(B). When step (A)(ii) is included the concentration in step (B) can bedetermined by simply determining the nitric oxide concentration of theair.

According to an eleventh embodiment of this invention there provided amethod for determining ozone concentration in air, which methodcomprises:

(A) determining nitric oxide concentration of the air;

(B) determining NO_(y) concentration of the air;

(C) determining concentration of smog in the air according to the methodof the third embodiment; and

(D) calculating the ozone concentration of the air from the measurednitric oxide concentration, NO_(y) concentration and the concentrationof smog in the

According to a twelfth embodiment of this invention there is provided amethod for determining nitric oxide and/or ozone concentrations in air,which method comprises:

(A) determining the sunlight intensity of the air;

(B) determining the temperature of the air;

(C) determining the NO_(y) concentration of the air;

(D) determining the smog concentration of the air according to themethod of the third embodiment; and

(E) determining the concentrations of nitric oxide and/or ozone in airfrom the NO_(y) and smog concentrations, the sunlight intensity and thetemperature.

Optionally the method of the twelfth embodiment further includesstep(B)(i); converting NO_(y) in the air to nitric oxide prior to step(C). When step (B)(i) is included the concentration in step (C) can bedetermined by simply determining the nitric oxide concentration of theair

According to a thirteenth embodiment of this invention there is provideda system for determining rate coefficient of smog formation in air,which system comprises:

(a) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(b) a first reactor operatively associated with the combiner wherein themixture can react in the first reactor for a first selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone in the mixture;

(c) a photoreactor operatively associated with the combiner andoptionally the first reactor;

(d) an illumination source operatively disposed about the photoreactorto illuminate the mixture of (a) in the photoreactor, or the mixtureafter the first selected period, in the photoreactor for a secondselected period under known temperature and illumination conditions;

(e) a second reactor operatively associated with the photoreactorwherein the mixture can react in the second reactor for a third selectedperiod wherein excess nitric oxide in the mixture reacts withsubstantially all ozone in the mixture;

(f) a nitric oxide analyser operatively associated with the firstreactor, to determine a first nitric oxide concentration of the mixtureafter the first selected period and operatively associated with thesecond reactor to determine a second nitric oxide concentration of themixture after the third selected period;

(g) a temperature sensor operatively associated with the photoreactor todetermine the temperature of the mixture;

(h) an illumination sensor operatively associated with the illuminationsource to determine the amount of illumination of the illuminatedmixture; and

(i) calculating means operatively associated with the temperature andillumination sensors and the nitric oxide analyser to calculate the ratecoefficient from the first and second nitric oxide concentrations, theknown temperature and illumination conditions and the duration of thesecond selected period.

According to a fourteenth embodiment of this invention there is provideda system for determining rate coefficient of smog formation in air,which system comprises:

(a) a first combiner for combining excess ozone with the air to providean excess ozone/air mixture;

(b) a first reactor operatively associated with the combiner wherein themixture can react in the first reactor for a first selected periodwherein excess ozone in the mixture reacts with substantially all nitricoxide in the mixture;

(c) a photoreactor operatively associated with the combiner andoptionally the first reactor;

(d) an illumination source operatively disposed about the photoreactorto illuminate the mixture of (a) in the photoreactor, or the mixtureafter the first selected period, in the photoreactor for a secondselected period under known temperature and illumination conditions;

(e) a second reactor operatively associated with the photoreactorwherein the mixture can react in the second reactor for a third selectedperiod wherein excess ozone in the mixture reacts with substantially allnitric oxide in the mixture;

(f) an ozone analyser operatively associated with the first reactor todetermine a first ozone concentration of the mixture after the firstselected period and operatively associated with the second reactor todetermine a second ozone concentration of the mixture after the thirdselected period;

(g) a temperature sensor operatively associated with the photoreactor todetermine the temperature of the mixture;

(h) an illumination sensor operatively associated with the illuminationsource to determine the amount of illumination of the illuminatedmixture; and

(i) calculating means operatively associated with the temperature andillumination sensors and the ozone analyser to calculate the ratecoefficient from the first and second ozone concentrations, the knowntemperature and illumination conditions and the duration of the secondselected period.

Optionally the system of the fourteenth embodiment further includes asecond combiner operatively associated with the first combiner forcombining a quantity of nitrogen oxides with the air.

According to a fifteenth embodiment of this invention there is provideda system for determining concentration of smog in air, which systemcomprises:

(a) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(b) a reactor operatively associated with the combiner wherein themixture can react in the reactor for a selected period wherein excessnitric oxide in the mixture reacts with substantially all ozone in themixture;

(c) a nitric oxide analyser operatively associated with the reactor todetermine the nitric oxide concentration of the mixture after theselected period;

(d) a NO_(y) analyser operatively associated with the reactor todetermine the NO_(y) concentration of the mixture; and

(e) calculating means operatively associated with the nitric oxideanalyser and the NO_(y) analyser to calculate the concentration of smogfrom the NO_(y) and nitric oxide concentrations.

Preferably the NO_(y) analyser of (d) includes a NO_(y) converter toconvert all NO_(y) in the mixture to nitric oxide, the converter beingoperatively associated with the nitric oxide analyser of (c). In thispreferred arrangement the NO_(y) analyser consists of the NO_(y)converter and the nitric oxide analyser of (c).

According to a sixteenth embodiment of this invention there is provideda system for determining amount of prior smog formation in air, whichsystem comprises:

(a) a first NO_(y) analyser to determine the NO_(y) concentration of theair;

(b) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(c) a reactor operatively associated with the combiner wherein themixture can react in the reactor for a selected period wherein excessnitric oxide in the mixture reacts with substantially all ozone in themixture;

(d) a nitric oxide analyser operatively associated with the reactor todetermine the nitric oxide concentration of the mixture after theselected period;

(e) a second NO_(y) analyser operatively associated with the reactor todetermine the NO_(y) concentration of the mixture; and

(f) calculating means operatively associated with the nitric oxideanalyser and the first and second NO_(y) analysers to calculate theamount of prior smog formation in air from the NO_(y) concentration ofthe air and the NO and NO_(y) concentrations of the excess nitricoxide/air mixture.

Preferably the NO_(y) analyser of (a) is the same NO_(y) analyseremployed in (e) operatively associated to the combiner of (b) so as todetermine the NO_(y) concentration of air before excess nitric oxide iscombined with air.

Also preferably the NO_(y) analyser of (a) and (d) includes a NO_(y)converter to convert all NO_(y) in the mixture to nitric oxide, theconverter being operatively associated with the nitric oxide analyser of(d). In this preferred arrangement the NO_(y) analyser consists of theNO_(y) converter and the nitric oxide analyser of (d).

According to a seventeenth embodiment of this invention there isprovided a system for determining maximum potential and optionally thecurrent extent of smog formation in air, which system comprises:

(a) a first NO_(y) analyser for determining the NO_(y) concentration ofthe air;

(b) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(c) a reactor operatively associated with the combiner wherein themixture can react in the reactor for a selected period wherein excessnitric oxide in the mixture reacts with substantially all ozone in themixture:

(d) a nitric oxide analyser operatively associated with the reactor todetermine the nitric oxide concentration of the mixture after theselected period:

(e) a second NO_(y) analyser operatively associated with the reactor todetermine the NO_(y) concentration of the mixture; and

(f) calculating means operatively associated and coupled with the nitricoxide analyser and the first and second NO_(y) analysers to calculatethe maximum potential and optionally the current extent of smogformation in air from the NO_(y) concentration of the air and the NO_(y)and NO_(Y) concentrations of the excess nitric oxide/air mixture.

Preferably the NO_(y) analyser of (a) is the same NO_(y) analyseremployed in (e) coupled to and operatively associated to the combiner of(b) so as to determine the NO_(y) concentration of air before excessnitric oxide is combined with air.

Also preferably the NO_(y) analyser of (a) and (e) includes a NO_(y)converter to convert all NO_(y) in the mixture to nitric oxide, theconverter being operatively associated with the nitric oxide analyser of(d). In this preferred arrangement the NO_(y) analyser consists of theNO_(y) converter and the nitric oxide analyser of (d).

According to an eighteenth embodiment of this invention there isprovided a system for determining rate of smog formation in air underselected temperature and illumination conditions, which systemcomprises:

(a) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(b) a first reactor operatively associated with the combiner wherein themixture can react in the first reactor for a first selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone in the mixture;

(c) a photoreactor operatively associated with the combiner andoptionally the first reactor;

(d) an illumination source operatively disposed about the photoreactorto illuminate the mixture of (a), in the photoreactor, or the mixtureafter the first selected period, in the photoreactor for a secondselected period under selected temperature and illumination conditions;

(e) a second reactor operatively associated with the photoreactorwherein the mixture can in the second reactor react for a third selectedperiod wherein excess nitric oxide in the mixture reacts withsubstantially all ozone in the mixture;

(f) a nitric oxide analyser operatively associated with the firstreactor to determine a first nitric oxide concentration of the mixtureafter the first selected period and operatively associated with thesecond reactor to determine a second nitric oxide concentration of themixture after the third selected period; and

(g) calculating means operatively associated with the nitric oxideanalyser to calculate the rate from the first and second nitric oxideconcentrations and the duration of the second selected period.

According to a nineteenth embodiment of this invention there is provideda system for determining rate of smog formation in air under selectedtemperature and illumination conditions, which system comprises:

(a) a first combiner for combining excess ozone is combined with the airto provide an excess ozone/air mixture;

(b) a first reactor operatively associated with the combiner wherein themixture can react in the reactor for a first selected period whereinexcess ozone in the mixture reacts with substantially all nitric oxidein the mixture;

(c) a photoreactor operatively associated with the combiner andoptionally the first reactor;

(d) an illumination source operatively disposed about the photoreactorto illuminate the mixture of (a), in the photoreactor, or the mixtureafter the first selected period, in the photoreactor for a secondselected period under selected temperature and illumination conditions;

(e) a second reactor operatively associated with the photoreactorwherein the mixture can react in the second reactor for a third selectedperiod wherein excess ozone in the mixture reacts with substantially allnitric oxide in the mixture;

(f) an ozone analyser operatively associated with the first reactor todetermine a first ozone concentration of the mixture after the firstselected period and operatively associated with the second reactor todetermine a second ozone concentration of the mixture after the thirdselected period; and

(g) calculating means operatively associated with the ozone analyser tocalculate the rate from the first and second ozone concentrations andthe duration of the second selected period.

In preferred embodiments of the thirteenth, fourteenth, eighteenth andnineteenth embodiments the first and second reactors and thephotoreactor are the same reactor. In other preferred embodiments thefirst reactor and the photoreactor are the same reactor and in yet otherembodiments the second reactor and the photoreactor are the samereactor.

In still other preferred embodiments the first reactor and photoreactorare two separate vessels through which the mixture can continuously flowin separate streams and the second reactor is a separate vessel throughwhich the mixture from the photoreactor can continuously flow.

In such embodiments, the first reactor provides a first residence timefor the mixture when continuously flowing therethrough and thephotoreactor and the second reactor in combination provide a secondresidence time for the mixture when continuously flowing therethrough,the first and second residence times being substantially the same.

Optionally the system of the nineteenth embodiment further includes asecond combiner operatively associated with the combiner of ozone inwhich second combiner a quantity of NO_(x) is added to air. This isrecommended when the nitric oxide concentration of air is small andlimiting on the rate of reaction in the photolytic reactor.

According to a twentieth embodiment of this invention there is provideda system for determining time required for maximum smog formation in airunder selected conditions of illumination and temperature wherein thesystem includes:

(A) a NO_(y) analyser to determine the NO_(y) concentration of the air;

(B) the system of the thirteenth or fourteenth embodiments to determinethe rate coefficient of smog formation in the air; or

(B)(i) the system of the eighteenth or nineteenth embodiments todetermine the rates of the smog formation in air under the selectedconditions;

(C) the system of the seventeenth embodiment to determine the maximumpotential smog formation in the air; and

(D) calculating means operatively associated with the analyser of (A)and the systems of (B) and (C) to calculate the maximum time for smogformation, under the selected temperature and illumination conditionsfrom the NO_(y) concentration, the extent of smog formation and the ratecoefficient; or

(D)(i) calculating means operatively associated with the analyser of (A)and the systems of (B)(i) and (C) to calculate the maximum time for smogformation, under the selected temperature and illumination conditionsfrom the NO_(y) concentration, the extent of smog formation and therates.

Preferably the NO_(y) analyser of (A) includes a NO_(y) converter toconvert all the NO_(y) in the air to nitric oxide and a nitric oxideanalyser to determine the total nitric oxide in this preferredarrangement the NO_(y) analyser consists of the NO_(y) converter and thenitric oxide analyser and the NO analysers of the systems of (A), (B) or(B)(i) and (C) are the same analyser,

According to a twenty-first embodiment of this invention there isprovided a system for determining time period during which smogformation in air has occurred, the time period being substantially thesame as or within a selected period for which the illumination andtemperature conditions are known, wherein the end of the selected periodcoincides with the end of the time period the system includes:

(A) the system of the thirteenth or fourteenth embodiments fordetermining the rate coefficient of smog formation in the air; or

(A)(i) the system of the eighteenth or nineteenth embodiments fordetermining the rates of smog formation in the air;

(B) the system of the fifteenth embodiment for determining concentrationof smog in the air;

(C) an NO_(y) analyser for determining the NO_(y) concentration of air;

(D) a temperature sensor to determine the temperature of the air for theduration of the selected period;

(E) a light sensor to determine the sunlight illumination during theselected period; and

(F) calculating means operatively associated with the temperaturesensor, the light sensor, the NO_(y) analyser and the systems fordetermining the rate coefficient of smog formation and smogconcentration, to calculate the time period during which smog formationin air has occurred under the measured sunlight and temperatureconditions; or

(F)(i) calculating means operatively associated with the temperaturesensor, the light sensor, the NO_(y) analyser and the systems of a(i)and (b) to calculate the time period during which smog formation hasoccurred under the measured sunlight and temperature conditions.

Preferably the NO_(y) analyser of (C) includes a NO_(y) converter toconvert all NO_(y) in the mixture to nitric oxide, the converter beingoperatively associated with a nitric oxide analyser. In this preferredarrangement the NO_(y) analyser consists of the NO_(y) converter and thenitric oxide analyser and the NO_(y) analysers of the systems of (A) and(B) and the NO analyser of (C) are the same analyser.

Optionally the system of the twenty-first embodiment further includesmeans of determining the speed and trajectory of the air during theselected period and calculating means to determine the location of theemission sources of ROC present in air on the basis of the time periodof smog formation, the air speed and trajectory.

According to a twenty-second embodiment of this invention there isprovided a system for determining time required for production of aselected amount of smog in air under selected temperature andillumination conditions the system comprising

(A) the system of the thirteenth or fourteenth embodiments fordetermining rate coefficient of smog formation in the air; or

(A)(i) the system of the eighteenth or nineteenth embodiments fordetermining the rates of smog formation in the air;

(B) the system of the fifteenth embodiment for determining concentrationof smog in the air;

(C) an NO_(y) analyser for determining the NO_(y) concentration of theair; and

(D) calculating means operatively associated with the systems fordetermining: the rate coefficient, smog concentration and the NO_(y)analyser, to calculate the time required for the production of aselected amount of smog in the air under selected temperature andillumination conditions; or

(D)(i) calculating means operatively associated with the systems of(A)(i) and (B) and the NO_(y) analyser, to calculate the time requiredfor the production of a selected amount of smog in air under selectedtemperature and illumination conditions.

Preferably the NO_(y) analyser of (C) includes a NO_(y) converter toconvert substantially all NO_(y) in the mixture to nitric oxide, theconverter being operatively associated with the nitric oxide analyser of(B). In this preferred arrangement the NO_(y) analyser consists of theNO_(y) converter and the nitric oxide analyser of (B).

According to a twenty-third embodiment of this invention there isprovided a system for determining ozone concentration in air whichsystem comprises:

(A) a nitric oxide analyser to determine the nitric oxide concentrationof the air;

(B) a NO_(y) analyser to determine the NO_(y) concentration of the air;

(C) the system of the fifteenth embodiment for determining theconcentration of smog in the air; and

(D) calculating means operatively associated with the nitric oxideanalyser of (A) the NO_(y) analyser of (B) and the system of (C) tocalculate the ozone concentration from the nitric oxide concentration,NO_(y) concentration and smog concentration of the air.

Preferably the nitric oxide analyser of (A) and the NO_(y) analyser of(B) are the same nitric oxide and NO_(y) analysers of the system of (C).

According to a twenty-fourth embodiment of this invention there isprovided a system for determining nitric oxide and NO_(y) or ozone orboth concentrations in air which system comprises:

(A) a light sensor to determine the sunlight intensity of the air;

(B) a temperature sensor to determine the temperature of the air;

(C) an NO_(y) analyser to determine the NO_(y) concentration of the air;

(D) the system of the fifteenth embodiment to determine the smogconcentration of the air; and

(E) calculating means operatively associated with the light andtemperature sensors and the NO_(y) analyser and smog concentrationmeasurement systems the calculating means to calculate the nitric oxideand ozone concentrations of the air from the sunlight intensity, airtemperature and the NO_(y) and smog concentrations.

Preferably the NO_(y) analyser of (C) is the same NO_(y) analyser of thesystem (D).

According to a twenty-fifth embodiment of this invention there isprovided a method for determining ROC concentration of air and/or amethod for determining total concentration of prior ROC emissions intoair, which method comprises:

(a) adding excess nitric oxide to the air to provide an excess nitricoxide/air mixture;

(b) permitting the mixture to react for a first selected period whereinexcess nitric oxide in the mixture reacts with substantially all ozonein the mixture;

(c) determining a first nitric oxide concentration of the mixture afterthe first selected period;

(d) illuminating the mixture of (a) or the mixture after the firstselected period for a second selected period under known temperature andillumination conditions;

(e) permitting the mixture, after illumination, to react for a thirdselected period wherein excess nitric oxide in the mixture reacts withany ozone present in the mixture;

(f) determining a second nitric oxide concentration of the mixture afterthe third selected period; and

(g) determining the ROC concentration of air, and/or determining thetotal concentration of prior ROC emissions into the air, from the firstand second nitric oxide concentrations

According to a twenty-sixth embodiment of this invention there isprovided a system for determining ROC concentration of air and/or totalconcentration of prior ROC emissions into air, which system comprises:

(a) a combiner for combining excess nitric oxide with the air to providean excess nitric oxide/air mixture;

(b) a first reactor operatively associated with the combiner wherein themixture can react in the first reactor for a first selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone in the mixture;

(c) a photoreactor operatively associated with the combiner andoptionally the first reactor;

(d) an illumination source operatively disposed about the photoreactorto illuminate the mixture of (a), in the photoreactor, or the mixtureafter the first selected period, in the photoreactor for a secondselected period under selected temperature and illumination conditions;

(e) a second reactor operatively associated with the photoreactorwherein the mixture can in the second reactor react for a third selectedperiod wherein excess nitric oxide in the mixture reacts withsubstantially all ozone in the mixture;

(f) a nitric oxide analyser operatively associated with the firstreactor to determine a first nitric oxide concentration of the mixtureafter the first selected period and operatively associated with thesecond reactor to determine a second nitric oxide concentration of themixture after the third selected period; and

(g) calculating means operatively associated with the nitric oxideanalyser to calculate the ROC concentration of air, and/or totalconcentration of prior ROC emissions into air, from the first and secondnitric oxide concentrations.

According to a further embodiment of this invention there is provided amethod of locating a source of Reactive Organic Compounds (ROC) presentin air, the method comprising:

(α) determining a time period during which smog formation in the air hasoccurred, the time period being substantially the same as or within apredetermined period for which the illumination and temperatureconditions are known, wherein the end of the predetermined periodcoincides with the end of the time period by:

(A) determining temperatures of the air for the predetermined period;

(B) determining sunlight intensities for the predetermined period;

(C) determining the rate coefficient of smog formation in the air by themethod described herein;

(D) determining the amount of prior smog formation in the air at the endof the time period by:

(I) determining NO_(y) concentration in the air;

(II) determining the concentration of smog in the air by:

(II)(i) adding excess nitric oxide to the air to provide an excessnitric oxide/air mixture;

(II)(ii) reacting the mixture for a selected period wherein the excessnitric oxide reacts with substantially all ozone in the mixture;

(II)(iii) determining the nitric oxide concentration of the mixtureafter the selected period;

(II)(iv) determining the total oxidized nitrogen (NO_(y)) concentrationof the mixture after the selected period; and

(II)(v) determining the concentration of smog formation from the nitricoxide concentration of (II)(iii) and the NO_(y) concentration of(II)(iv).

(III) determining the concentration of total nitrogen oxides previouslyemitted into the air from the NO_(y) concentration in the air and theconcentration of smog in the air; and (IV) determining the amount ofprior smog formation in the air from the concentration of total nitrogenoxides previously emitted into the air as determined in step (III) andthe concentration of smog in the air as determined in (II); and

(E) determining the time period during which the smog formation in theair has occurred from the amount of prior smog formation, the ratecoefficient, and the determined temperatures and sunlight intensities;and

(β) determining speed of movement and trajectory in the air during thetime period; and

(γ) locating said source of ROC from said time period and said speed andtrajectory in the air over said time period.

According to a still further embodiment of this invention there isprovided a method for determining the current extent of smog formationin air, which method comprises the steps of:

(I) determining maximum potential smog formation in air by the method ofthe fifth embodiment; and

(II) calculating the extent of smog formation in air as the ratio of theconcentration of smog in air to the maximum potential concentration ofsmog in air.

The temperature of the mixture can be kept constant during illumination,can be allowed to vary and optionally monitored or the temperature ofthe mixture can be varied according to a preselected or selectedtemperature profile. Thus, it is preferred that a temperaturecontroller/programmer is operatively associated with the photoreactorsof the thirteenth, fourteenth, eighteenth, nineteenth and twenty-sixthembodiments.

The illumination can be kept constant or can be varied according to apreselected or selected illumination profile. It is therefore preferredthat an illuminator controller/programmer is operatively associated withand coupled with the illumination sources of the thirteen, fourteenth,eighteenth, nineteenth and twenty-sixth embodiments.

Preferred illumination sources provide an actinic flux of similarintensity and spectral distribution to sunlight at about noon on a clearday. It may be adequate for the purpose, however, to approximate thesolar spectrum by only the "UVA" part of the total wavelength band.

Illumination may be provided by a single type of lamp or various lamptype and filter combinations. For example, actinic UV fluorescent tubesare suitable as is a high pressure xenon arc and pyrex glass filtercombination. The preferred illumination intensity is that which yields arate coefficient for the photodissociation of nitrogen dioxide (NO₂+hν→NO+O) of ˜0.4 min⁻¹. However intensities which depart markedly fromthis value are viable. Times preferred for the first and third reactionperiods are of tile order of a few minutes, which is sufficient for thereaction of nitric oxide with ozone to be substantially complete. Thepreferred time for the second selected period is about 10 minutes or solong as is required to produce measurable consumption of nitric oxide inair containing significant quantity of ROC.

The systems of the thirteenth, fourteenth, fifteenth, sixteenth,seventeenth, eighteenth, nineteenth and twenty-sixth embodimentsoptionally include first metered delivery means to deliver metered dosesof air to the combiner and includes second metered delivery means todeliver metered doses of nitric oxide to the combiner.

The fourteenth and nineteenth embodiments optionally include thirdmetered delivery means to deliver metered doses of ozone to the combinerand ozone filter to filter ozone prior to injection into the combiner.

Optionally the systems of the thirteenth, fourteenth, fifteenth,sixteenth, seventeenth, eighteenth, nineteenth and twenty-sixthembodiments include an air filter to filter air prior to injection intothe combiner and a nitric oxide filter to filter nitric oxide prior toinjection into the combiner.

It is preferred that the photoreactor is constructed from material thatis transparent to illumination and is chemically unreactive. FEP teflonfilm is an example of material which is suitable for this purpose.

FEP teflon film has the advantages that it is chemically unreactive andis transparent to ultraviolet light and is available in thin but robustfilm form.

The concentration of nitric oxide excess in the nitric oxide/air mixtureor ozone excess in the ozone/air mixture is typically in the range about0.05 to about 1 ppm (mole fraction) but the upper range limit should notbe of a concentration which induces reactions to occur in the mixturewhich result in a significant change in the nature of the chemistry ofthe mixture. For example, a large excess of nitric oxide can cause areduction in the hydroxyl radical concentration of the photoreactor,resulting in a reduction in the rate of nitric oxide consumption in thephotoreactor. The lower range limit should be sufficient to provide forcomplete reaction of the ozone or nitric oxide of the air with theexcess nitric oxide or ozone respectively. More typically the range isabout 0.05 to about 0.3 ppm and even more typically about 0.05 to about0.15 ppm. Preferably the concentration is about 0.1 ppm.

GENERAL DESCRIPTION OF THE METHOD OF CALCULATION

Whilst photochemical smog formation is the result of some severalhundred or more elementary reaction steps in the light of the presentinventor's finding that the amount of smog formed in air and the smogconcentration in air can be determined by the oxidation of NO, theoverall reactions of smog formation can be described by the followingrepresentative expressions: ##STR2## where RO₂ denotes hydroxyl, alkoxyand peroxy free radical species, ROC and ROC' are "reactive organiccompounds" including carbonyl, alkane, alkene, aromatic, carbon monoxideand other types of gas phase carbonaceous species which when present andilluminated in air undergo reactions whereby oxygen is consumed and NOis oxidized, NO_(x) denotes NO and NO₂ and n is a proportionalitycoefficient.

Providing there is sufficient illumination, reactions (2), (3) and (4)continue until the NO concentration is reduced to such a level thatthere is insufficient NO available to freely maintain reaction (2) andsmog formation is curtailed. In addition to RO₂ reaction with NO, freeradicals produced by reaction (1) may also undergo radical-radicalrecombination via reaction (5). During smog formation ROC molecules maycycle through reaction (1) several times. Although the constituentspecies of ROC are changed by participation in the reactions, to a goodapproximation for air of ROC composition as usually found in urbanregions, the rate coefficient for reaction (1) remains surprisinglyconstant, independently of the extent of reaction and at least forillumination intensities and durations equivalent to the sunlight of anunclouded summer's day.

Nitric oxide undergoes reaction with free radical species via reactions(2), (6) and (7). However in general the rate of NO reaction via (2) ismuch greater than the rate of NO reaction via (6) and (7). For manypurposes NO reaction by (6) and (7) can be neglected.

Reaction of NO in accordance with reactions (2), (6) and (7) is ameasure of smog formation. The rate of NO consumption by these reactionsis a measure of the rate of smog formation while the concentration of NOso consumed is a measure of the smog concentration.

In illuminated air NO consumed by reaction (2) can be regenerated byreaction (3), producing moles of O₃ equivalent to the NO regenerated. Bythe addition of excess NO to air, O₃ is reacted according to reaction(4) with the consumption of equivalent NO.

The moles of smog formed in air up to time t, (^(f) n_(smog) ^(t)), thatis the number of moles of NO consumed by reaction (2), is determined asbeing equal to the total number of moles of NO emitted into the air(^(o) n_(NO) ^(t)) up to time t plus moles of excess nitric oxide addedduring analysis (^(added) n_(NO)) less the moles of nitric oxideremaining after completion of reaction (4) in the analysis system (^(I)n_(NO)):

    .sup.f n.sub.smog.sup.t =.sup.o n.sub.NO.sup.t +.sup.added n.sub.NO -.sup.I n.sub.NO                                                  ( 8)

While there are many nitrogenous species known to be present in air andconstituting NO_(y) it is usual for NO_(y) to be emitted into the air inonly two forms, namely NO and NO₂ and these emissions together arecommonly denoted as NO_(x) :

    NO.sub.x =NO+NO.sub.2.                                     (9

Furthermore, the bulk of all anthropogenic NO_(x) emissions are in theform of NO. The fraction of NO in NO_(x) emissions (^(o) F_(NO)) canvary with the specific type of NO_(x) emission source ( e.g. the burntgases from furnaces, motor vehicles, domestic heating) but commonlyfalls within the range 0.6 to 1.0. For urban atmospheres the value of^(o) F_(NO) is frequently in the range of 0.7 to 0.95. However, ^(o)F_(NO) can be determined explicitly by measurement of the NO/NO_(x)composition of the NO_(x) emissions at their source.

Thus the NO emitted into the air can be determined as a function of theemission of NO_(y) into the air, since for emissions:

    .sup.o n.sub.NO.sup.t.sbsb.y =.sup.o n.sub.NO.sup.t.sbsb.x ( 10)

hence

    .sup.o n.sub.NO.sup.t =.sup.o F.sub.NO.sup.o n.sub.NO.sbsb.y.sup.t( 11)

and to a fair approximation ^(o) F_(NO) has the value of 0.9.

NOTE: For some purposes it is sufficiently accurate to employ the value1 for ^(o) F_(NO), in which case:

    .sup.o n.sub.NO.sup.t ≈.sup.o n.sub.NO.sbsb.y.sup.t( 12)

During smog formation some NO_(y) is lost from the air by reaction (7),some NO_(y) being incorporated into nongaseous nitrogenous species, thusthe NO_(y) content of the air at time t, (n_(NOy) ^(t)) aftersignificant t smog forming reaction has taken place, may be less thanthe amount of NO_(y) emitted into the air (^(o) n_(NO).sbsb.y^(t)). Therate of NO_(y) loss from the air is slow compared to the rate of smogformation and so for many purposes the NO_(y) loss is relatively smalland can be neglected, i.e.:

    .sup.o n.sub.NOt.sbsb.y.sup.t ≈n.sub.NO.sbsb.y.sup.t( 13)

In daylight and for air with compositions as commonly found in urbanregions, reaction (7) proceeds at a rate (R₇) and which is a function ofthe rate of reaction (2), (R₂):

    R.sub.7 =f(R.sub.2)                                        (14)

To a good approximation the form of the function f(R₂) is one of directproportion:

    R.sub.7 =P.sub.7,2 R.sub.2                                 ( 15)

where P₇,2 is the proportionality coefficient. A typical value for P₇,2is determined by the inventor to be 0.125. Thus optionally (15) and themeasured value of n_(NO).sbsb.y^(t) may be used to obtain a moreaccurate estimate of ^(o) n_(NO).sbsb.y^(t) in place of (13).

The concentration of smog in air is a function of: the rate of smogformation, the pre-existing smog concentration, the dispersion anddilution of the air by meteorological processes and the loss of smogfrom the air by the deposition of ozone and NO_(y) species,incorporation of NO_(y) into particulate materials and other lossprocesses.

Defining smog concentration to be the sum of the concentrations of thegaseous oxidized nitrogen species, plus the ozone concentration, lessthe concentration of nitric oxide, the smog concentration of air at timet, χ_(smog) ^(t) is determined by the method of the third embodiment andby means of the system of the fifteenth embodiment, namely from the NOconcentration of the mixture after the selected period of the thirdembodiment, step (c) (^(I) χ_(NO)) and the total oxidized nitrogenconcentration of the mixture at step (d), (^(I) χ_(NO).sbsb.y), by theequation:

    χ.sub.smog.sup.t =.sup.I χ.sub.NO.sbsb.y -.sup.I χ.sub.NO( 16)

Defining the amount of smog formation in volume V^(t) of air at time t,(^(f) n_(smog) ^(t)), to be the number of moles of NO previouslyconsumed by reaction (2), (6) and (7) ^(f) n_(smog) ^(t), is given byequation (17):

    .sup.f n.sub.smog.sup.t =.sup.o n.sub.NO.sup.t +n.sub.O.sbsb.3.sup.t -n.sub.NO.sup.t                                           ( 17)

and from (10) and (11):

    .sup.o n.sub.NO.sup.t =.sup.o F.sub.NO.sup.o n.sub.NO.sbsb.y.sup.t( 18)

and from (15), correcting the NO_(y) content of air for loss of NO_(y)from the air by reaction (7):

    .sup.o n.sub.NO.sbsb.y.sup.t =n.sub.NO.sbsb.y.sup.t +P.sub.7,2.sup.f n.sub.smog.sup.t                                          ( 19)

Substituting (19) for ^(o) n_(NO).sbsb.y^(t) in (18)

    .sup.o n.sub.NO.sup.t =.sup.o F.sub.NO (n.sub.NO.sbsb.y.sup.t +P.sub.7,2.sup.f n.sub.smog.sup.t)                        (20)

Substituting (20) in (17) and rearranging

    .sup.f n.sub.smog.sup.t =(.sup.o F.sub.NO n.sub.NO.sbsb.y.sup.t +n.sub.O.sbsb.3.sup.t -n.sub.NO.sup.t)/ (1-.sup.o F.sub.NO P.sub.7,2)(21)

Now in the presence of excess added NO(^(added) n_(NO)) and afterreaction in darkness for a selected period such that reaction (4) iscomplete

    .sup.o F.sub.NO n.sub.NO.sbsb.y.sup.t +n.sub.O.sbsb.3.sup.t -n.sub.NO.sup.t =.sup.o F.sub.NO n.sub.NO.sbsb.y.sup.t +.sup.added n.sub.NO -.sup.I n.sub.NO.sup.t                                            ( 22)

now the amount of NO_(y) present after the selected period (^(I)n_(NO).sbsb.y) and addition of excess NO is given by:

    .sup.I n.sub.NO.sbsb.y =n.sub.NO.sbsb.y.sup.t +.sup.added n.sub.NO( 23)

hence

    .sup.o F.sub.NO n.sub.NO.sbsb.y.sup.t +.sup.added n.sub.NO =.sup.I n.sub.NO.sbsb.y -(1-.sup.o F.sub.NO)n.sub.NO.sbsb.y.sup.t ( 24)

substituting (24) into (22):

    .sup.o F.sub.NO n.sub.NO.sbsb.y.sup.t +n.sub.O.sbsb.3.sup.t -n.sub.NO.sup.t =.sup.I n.sub.NO.sbsb.y -(1-.sup.o F.sub.NO)n.sub.NO.sbsb.y.sup.t -.sup.I n.sub.NO                                                  ( 25)

and substituting (25) into (21):

    .sup.f n.sub.smog.sup.t =[.sup.I n.sub.NO.sbsb.y -.sup.I n.sub.NO -(1-.sup.o F.sub.NO)n.sub.NO.sbsb.y.sup.t ]/[1-.sup.o F.sub.NO P.sub.7,2 ](26)

Now Dalton's Law states for ideal gases, concentration (mole fraction)of species i at time t (χ_(i) ^(t)) is given by:

    χ.sub.i.sup.t =n.sub.i.sup.t RT.sup.t /P.sup.t V.sup.t ( 27)

where R is the gas constant and T^(t), P^(t) and V^(t) are thetemperature pressure and volume of the gas respectively at time t.Multiplying throughout (26) by RT^(t) /P^(t) V^(t) and substituting(27):

    .sup.f χ.sub.smog.sup.t =[.sup.I χ.sub.NO.sbsb.y -.sup.I χ.sub.NO -(1-.sup.o F.sub.NO) χ.sub.NO.sbsb.y.sup.t ]/[1-.sup.o F.sub.NO P.sub.7,2 ]                                      (25)

    for:

    .sup.f χ.sub.smog.sup.t <.sup.fmax χ.sub.smog

where ^(f) χ_(smog) ^(t) denotes the concentration of smog that would bepresent in the absence of NO_(y) loss from the air by reaction (7).

Equation (28) is valid for values of ^(f) χ_(smog) ^(t) less than themaximum potential smog formation (^(fmax) χ_(smog) ^(t)) but after thesmog maximum has been reached NO_(y) loss processes continue and newsmog is not formed. In this circumstance P₇,2 can no longer beapproximated by a value of 0.125. Now:

    χ.sub.smog.sup.t =.sup.I χ.sub.NO.sbsb.y -.sup.I χ.sub.NO( 16)

Substituting (16) into (28):

    .sup.f χ.sub.smog.sup.t [χ.sub.smog.sup.t -(1-.sup.o F.sub.NO)χ.sub.NO.sbsb.y.sup.t ]/[1-.sup.o F.sub.NO P.sub.7,2 ](29)

    for:

    .sup.f χ.sub.smog.sup.t <.sup.fmax χ.sub.smog.sup.t

Optionally, the approximations:

    .sup.o F.sub.NO ≈1

    and

    P.sub.7,2 ≈0

    can be made, then (29)yields:

    χ.sub.smog.sup.t ≈.sup.f χ.sub.smog.sup.t  ( 30)

Summarizing, the smog concentration in air (χ_(smog) ^(t)) is determinedby the system of the fifteenth embodiment and the method of the thirdembodiment and calculated from equation (16), i.e.

    χ.sub.smog.sup.t =.sup.I χ.sub.NO.sbsb.y -.sup.I χ.sub.NO( 16)

The NO_(y) concentration of the air may also be measured as per thefourth and sixteenth embodiments and the smog formation expressed as thenotional concentration of smog formed in air in the absence of smogremoval processes (^(f) χ_(smog) ^(t)) as calculated by equation (29):

    .sup.f χ.sub.smog.sup.t =[χ.sub.smog.sup.t -(1-.sup.o F.sub.NO)χ.sub.NO.sbsb.y.sup.t ]/(1-.sup.o F.sub.NO P.sub.7,2)(29)

    for:

    .sup.f χ.sub.smog.sup.t <.sup.fmax χ.sub.smog.sup.t

    where for most circumstances

    .sup.o F.sub.NO =0.9

    and

    P.sub.7,2 =0.125

    and

    P.sub.7,2 =0.125

The maximum potential smog formation in air is controlled by the rate ofreaction (2) relative to the combined rates of reactions (6) and (7).When reactions (6) and (7) have consumed NO₂ such that reaction (3)cannot regenerate NO in sufficient concentration to maintain reaction(2) smog formation is curtailed and new smog production eventuallyceases. Thus to a fair approximation the maximum potential smogformation in air (^(fmax) χ_(smog) ^(t) and ^(fmax) n_(smog) ^(t)) isgiven by:

    .sup.fmax χ.sub.smog.sup.t =β.sup.o χ.sub.NO.sbsb.y.sup.t( 31)

    .sup.fmax n.sub.smog.sup.t =β.sup.o n.sub.NO.sbsb.y.sup.t( 32)

where the function B is dependent on the rate of reaction (2) relativeto the combined rates of reactions (6) and (7) and for air ofcompositions commonly found in urban areas can be approximated by thevalue B: 4.

Substituting expressions (19) and (27) into equation (31) andrearranging yields expression for maximum potential concentration ofsmog formed in air in terms of the observables χ_(NO).sbsb.y^(t) and^(f) χ_(smog) ^(t) where ^(f) χ_(smog) ^(t) is given by equation (29):

    .sup.fmax χ.sub.smog.sup.t =β(χ.sub.NO.sbsb.y.sup.t +P.sub.7,2.sup.f χ.sub.smog.sup.t)                    (33)

    when

    (.sup.f χ.sub.smog.sup.t <.sup.fmax χ.sub.smog.sup.t)

The total maximum potential concentration of smog (^(Tmax) χ_(smog)^(t)) in air is defined as the sum of the concentrations of smog formedin air by smog formation processes plus the concentration of smogemitted into air as NO₂ :

    .sup.Tmax χ.sub.smog.sup.t =.sup.fmax χ.sub.smog.sup.t +.sup.o χ.sub.NO.sbsb.2.sup.t                                 ( 115)

where ^(o) χ_(NO).sbsb.2^(t) is the concentration of NO₂ emissions intoair.

Now from equations (9), (10), (11) and (27)

    .sup.o χ.sub.NO.sbsb.2.sup.t =(1-.sup.o F.sub.NO).sup.o χ.sub.NO.sbsb.y.sup.t                                 ( 116)

substituting (116) into (115)

    .sup.Tmax χ.sub.smog.sup.t =.sup.fmax χ.sub.smog.sup.t +(1-.sup.o F.sub.NO).sup.o χ.sub.NOy.sup.t                       ( 117)

and substituting (31) into (117) gives

    .sup.Tmax χ.sub.smog.sup.t =.sup.o χ.sub.NO.sbsb.y.sup.t (β+1-.sup.o F.sub.NO)                                (118)

By equations (19) and (27) equation (118) can be expressed as

    .sup.Tmax χ.sub.smog.sup.t =(β+1-.sup.o F.sub.NO)(χ.sub.NO.sbsb.y.sup.t +P.sub.7,2.sup.f χ.sub.smog.sup.t)(119)

    when

    (.sup.f χ.sub.smog.sup.t <.sup.fmax χ.sub.smog.sup.t)

where ^(f) χ_(smog) ^(t) is given by equation (29) .

The extent of smog formation at time t, (E_(smog) ^(t)), is given by:

    E.sub.smog.sup.t ≦(.sup.f n.sub.smog.sup.t /.sup.fmax n.sub.smog.sup.t)                                         (34)

    and

    E.sub.smog.sup.t =(.sup.f χ.sub.smog.sup.t /.sup.fmax χ.sub.smog.sup.t)                                     (35)

Rate of smog formation at selected temperature (T) and illuminationintensity (I) (^(T),I Q_(smog) ^(t)) in the presence of excess NO isgiven by:

    .sup.T,I Q.sub.smog.sup.t =(.sup.I χ.sub.NO -.sup.III χ.sub.NO)/.sup.II t                                   (36)

where ^(III) χ_(NO) and ^(I) χ_(NO) are the concentrations of NO afterthe third and first selected periods and ^(II) t is the duration of thesecond selected period of embodiments six and eighteen. The rate ^(T),IQ_(smog) ^(t) corresponds to the rate of NO consumption by reactions(2), (6) and (7).

The NO₂ produced by reaction (2) can react further via reaction (3) andsmog formation is then exhibited as ozone production. When excess ozoneis present the steady state NO concentration maintained by reactions (3)and (4) is small and then to a good approximation the increase in ozoneconcentration resulting from smog formation is quantitatively equal tothe NO consumed by reaction (2) less the NO_(x) consumed by reactions(6) and (7). In this circumstance the rate of smog formation is givenby:

    .sup.T,I A.sub.smog.sup.t =(.sup.I χ.sub.O.sbsb.3 -.sup.III χ.sub.O.sbsb.3)/(.sup.II t{1-1/β})               (37)

where ^(III) χ_(O).sbsb.3 and ^(I) χ_(o).sbsb.3 are the concentrationsof ozone after the third and first selected period and ^(II) t is theduration of the second period of embodiments seven and nineteen and G isa term to account for the NO_(x) consumed by reactions (6) and (7).Typically a suitable value for β is β=4.

Rate coefficient for smog formation R_(smog) ^(t) is given by:

    R.sub.smog.sup.t =.sup.T,I Q.sub.smog.sup.t /I.sup.t f(T.sup.t)(38)

where I^(t) and T^(t) are the illumination intensity and temperatureduring the second selected period of embodiments one or two or thirteenor fourteen. f(T^(t)) is a function of temperature and ^(T),I_(Q)_(smog) ^(t) is obtained by the method of the first or secondembodiments and the system of the thirteenth or fourteenth embodimentsand equations (36) or (37) respectively, and the function f(T^(t)) canbe adequately approximated by the expression:

    f(T.sup.t)=e.sup.-1000γ(1/T.spsp.t.sup.-1/316)       ( 39)

where y has the value of 4.7 and T is temperature in degrees Kelvin.

Alternatively, f(T^(t)) may be evaluated by measurement of ^(T),IQ_(smog) ^(t) over a range of temperatures. The value of R_(smog) ^(t)is dependent on the concentration and properties of the ROC content ofair and: ##EQU1## where a_(ROC)(i) is an activity coefficient for smogformation by ROC(i) and wherein ROC(i) can be an individual ROC or amixture of various ROC's. Smog formation is described by the equations:##EQU2## where

    .sup.T,I Q.sub.smog.sup.t =R.sub.smog.sup.t I.sup.t f(T.sup.t)(43)

    where

    (.sup.f χ.sub.smog.sup.t <β.sup.o χ.sub.NO.sbsb.y.sup.t)

    or

    .sup.T,I.sub.Q.sub.smog.sup.t =0(.sup.f χ.sub.smog.sup.t ≮β.sup.o χ.sub.NO.sbsb.y.sup.t)

Time required for selected amount of smog formation, for example: timefor maximum smog formation, embodiments 8 and 20; time period duringwhich smog formation has occurred, embodiments 9 and 21; or timerequired for production of a given amount of smog in air, embodiments 10and 22, may be calculated for selected or measured I^(t) and T^(t) viaequations (39), (42) and (43).

The ozone concentration of air is given by:

    χ.sub.O.sbsb.e.sup.t =χ.sub.smog.sup.t +χ.sub.NO.sup.t -χ.sub.NO.sbsb.y.sup.t                                ( 44)

where smog concentration χ_(smog) ^(t) and nitric oxide concentrationχ_(NO) ^(t) and the NO_(y) concentration χ_(NO).sbsb.y^(t) aredetermined by the method of the eleventh embodiment and the system ofthe twenty third embodiment.

When air is illuminated the concentrations of ozone and nitric oxide inthe air are interrelated and dependent on the intensity of light.According to reactions (3) and (4): ##STR3## when air is illuminatedthere is rapid exchange of oxygen atoms between NO₂ and O₃. In sunlightthe rates of reactions (3) and (4) are much faster than the rates ofreactions (2) (6) and (7). Thus the rates of reactions (3) and (4) areapproximately equal, i.e.:

    k.sub.e.sup.t χ.sub.NO.sbsb.2.sup.t =k.sub.4.sup.t χ.sub.NO.sup.t χ.sub.O.sbsb.3.sup.t                                  ( 64)

where K₃ ^(t) and K₄ ^(t) are the rate coefficients at t%me t for treactions (3) and (4) respectively and k₃ ^(t) incorporates theillumination intensity. For ambient air, the sunlight intensity isusually sufficiently steady for equation (64) to be valid.

From equation (64) and by definition of NO_(x) (equation (9))

    χ.sub.O.sbsb.3.sup.t =(χ.sub.NO.sbsb.x.sup.t -χ.sub.NO.sup.t)k.sub.3.sup.t /k.sub.r.sup.t χ.sub.NO.sup.t ( 124)

Substituting (124) into equation (44) and rearranging gives

    (χ.sub.NO.sup.t).sup.2 -(χ.sub.NO.sbsb.y.sup.t -χ.sub.smog.sup.t -k.sub.e.sup.t /k.sub.r.sup.t)χ.sub.NO.sup.t -k.sub.3.sup.t χ.sub.NO.sbsb.x.sup.t /k.sub.4.sup.t =O(125)

By an analogous argument an expression for χ_(O).sbsb.3^(t) can also bederived:

    k.sub.r.sup.t (χ.sub.o.sbsb.3.sup.t).sup.2  + (k.sub.3.sup.t  - k.sub.4.sup.t χ.sub.smog.sup.t  + k.sub.4.sup.t χ.sub.NO.sbsb.y.sup.t)χ.sub.o.sbsb.3.sup.t  + k.sub.3 (χ.sub.NO.sbsb.y.sup.t  - χ.sub.smog.sup.t  - χ.sub.NO.sbsb.x.sup.t  )= O                           (126)

Experimental observation of smog formation under natural sunlightconditions and concentrations simulating ambient air shows that when^(f) χ_(smog) ^(t) falls outside the range:

    (.sup.o χ.sub.NO.sup.t -H.sup.o χ.sub.NO.sbsb.y.sup.t)<.sup.f χ.sub.smog.sup.t <(.sup.o χ.sub.NO.sup.t +L.sup.o χ.sub.NO.sbsb.y.sup.t)                                (70)

where appropriate values for coefficients H and L are H=L=1/2 then theterms involving k₃ of equations (125) and (126) have only a smallinfluence on the values of χ_(NO) ^(t) and χ_(O).sbsb.3^(t), as is alsothe case in darkness (i.e. k₃ ^(t) =0). In these cases equation 25simplifies to

    χ.sub.NO.sup.t  = χ.sub.NO.sbsb.y.sup.t  - χ.sub.smog.sup.t (χ.sub.smog.sup.t  < χ.sub.NO.sbsb.y.sup.t)

    or

    χ.sub.NO.sup.t  = 0(χ.sub.smog.sup.t  ≧ χ.sub.NO.sbsb.y.sup.t)                                (68)

and equation 126 simplifies to

    χ.sub.o.sbsb.3.sup.t  = 0(χ.sub.smog.sup.t  ≦ χ.sub.NO.sbsb.y.sup.t)

    or

    χ.sub.o.sbsb.3.sup.t  = χ.sub.smog.sup.t  - χ.sub.NO.sbsb.y.sup.t (χ.sub.smog.sup.t  < χ.sub.NO.sbsb.y.sup.t)                                (69)

When ^(f) χ_(smog) ^(t) falls within the domain given by (70) and k₃^(t) ≠O then experimental study of smog formation under conditionspertinent to ambient air demonstrates that

    χ.sub.NO.sbsb.y.sup.t ≈χ.sub.NO.sbsb.x.sup.t( 71)

(when ^(f) χ_(smog) ^(t) is in the (domain given by expression (70)).

Then substitution of χ_(NO).sbsb.y^(t) for χ_(NO).sbsb.x^(t) inequations (125) and (126) is appropriate and, taking the value of k₄from the literature, enables the values of χ_(NO) ^(t) andχ_(O).sbsb.3^(t) to be evaluated.

Thus from measurements according to the method of embodiment twelve andthe system of embodiment twenty-four and equations (68), (69), (71),(125) and (126) the ozone and nitric oxide concentrations of the air aredetermined.

BRIEF DESCRIPTION OF DRAWINGS

Preferred embodiments of the systems and methods of this invention aredescribed below with reference to the following drawings in which:

FIG. 1 is a block diagram of a system for determining rate coefficientof smog formation in

FIG. 2 is a block diagram of a system for determining concentration ofsmog in air;

FIG. 3 is a block diagram of a system for determining rate of smogformation in air and also for determining ROC concentration of air andtotal concentration of prior ROC emissions into air;

FIG. 4 is a block diagram of an alternative system for determining ratecoefficient of smog formation in air; smog concentration, amount ofprior smog formation, maximum potential smog concentration, extent ofsmog formation, rate of smog formation under selected temperature andillumination conditions, NO_(y), O₃ and nitric oxide concentrations ofNO/NO_(x) concentration ratio of the NO_(x) previously introduced intoair, time period required for maximum smog formation, ROC content ofROC/NO_(x) concentration ratio of total previous introductions into air,total concentrations of ROC, NO_(y) and NO_(x) previously introducedinto air, time period during which smog formation has occurred, averagetime of previous introductions of ROC into air, and time period requiredfor production of selected amount of smog in air;

FIG. 5 is a block diagram of a further alternative system fordetermining rate coefficient of smog formation in air;

FIG. 6 is a block diagram of an alternative system for determining rateof smog formation in air;

FIG. 7 is a block diagram of a system for determining maximum potentialextent of smog formation in air and determining current extent of smogformation in air.

FIG. 8 is a schematic diagram of a preferred photoreactor for use in asystem of the invention; and

FIG. 9 is a schematic cross-section of the edge of the photoreactor ofFIG. 8.

FIG. 10 is a block diagram of a prefer-red nitric oxide analyser.

FIG. 11 is partially sectional plan view of the sample selection valvewhich together with the radial flow chemiluminescent reactor are twocomponents preferably used in the nitric oxide analyser of FIG. 10 aswell as a section view along A-A of the plan view.

FIG. 12 is a block diagram of a system similar to the system depicted inFIG. 4 and which was used in an Example run.

FIG. 13 is a plot of ^(CI) χ_(NO) ^(t) -^(CII) χ_(NO) ^(t) vs te^(-k)90^(t) which was used to calibrate the illumination source of the systemdepicted in FIG. 12.

BEST MODE AND OTHER MODES FOR CARRYING OUT THE INVENTION

Referring to FIG. 1 a system 10 for determining rate coefficient of smogformation in air includes an air filter II which filters incoming airand a metered delivery injector 12 which delivers a metered dose of thefiltered air to combiner 13. A metered dosage of excess nitric oxide iscombined with the filtered air in combiner 13 after passing throughnitric oxide filter 14 and being injected therein by metered deliveryinjector 15. As a result an excess nitric oxide/air mixture is formed incombiner 13 and dispensed via two separate streams. The concentration ofnitric oxide at injector 15 is typically a high concentration so thatthe volume of mixture produced by combiner 13 is close to the volume ofair from which it is generated, i.e. so that the volume of nitric oxiderequired to produce the excess nitric oxide/air mixture is smallcompared to the volume of air to which it is added and thus the volumeof nitric oxide added can be neglected for computational purposes.

Reactor 16 in which the mixture can react for a first selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone in the mixture is operatively coupled to combiner 13.

Photoreactor 17 is also operatively coupled to combiner 13. Illuminationsource 18 is operatively disposed,about photoreactor 17 to illuminatethe mixture in photoreactor 17 for a second selected period under knowntemperature and illumination conditions. Illumination from source 18 canbe kept constant or can be varied according to a preselected or selectedillumination profile. Illumination controller/programmer 19 isoperatively coupled to source 18 and an illumination sensor consistingof photodiode 20 and photometer 21 for this latter purpose.

Temperature sensor 22 is operatively coupled to photoreactor 17 andtemperature controller/programmer 23 to determine the temperature of themixture in photoreactor 17. The temperature of the mixture inphotoreactor 17 can be kept constant during illumination or can beallowed to vary and monitored or can be varied according to apreselected or selected temperature profile by temperaturecontroller/programmer 23 which is operatively coupled to photoreactor 17via lines 24 and 25. A reactor 29 in which during a third selectedperiod excess nitric oxide of the mixture reacts with substantially allozone is operatively coupled to photoreactor 17.

Nitric oxide analyser 26 is operatively coupled to reactor 16 todetermine a first nitric oxide concentration of the mixture after thefirst selected period at point CI and operatively coupled to reactor 29to determine a second nitric oxide concentration of the mixture afterthe third selected period at point CII. The mixture is vented from thesystem via analyser 26 and vent 27. Computer 28 is operatively coupledto temperature sensor 22, photometer 21 and analyser 26 to calculate therate coefficient from the first and second nitric oxide concentrations,the known temperature and illumination conditions and the duration ofthe second selected period.

Typically reactor 16 is of similar form and volume as the combination ofthe reaction vessels of photoreactor 17 and reactor 29 and the residencetime for the mixture to pass from combiner 13 to CI is the same as thetime required to pass from combiner 13 to CII. By this means themixtures available at CI and CII have a common origin at combiner 13.Thus, when the composition of air entering filter 11 has components ofrapidly varying concentration the mixtures at CI and CII have a commonorigin from air of identical compositions.

The rate coefficient of smog formation in air can be determined in Thefollowing manner. A metered amount of air is delivered to combiner 13,after passing through filter 11 and injector 12. Excess nitric oxide isadded to the air in combiner 13, after passing through filter 14, andinjector 15 to provide an excess nitric oxide/air mixture in combiner13. The mixture is transferred to reactor 16 and photoreactor 17. Themixture is permitted to react in reactor 16 for a first selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone the mixture. A first nitric oxide concentration of the mixture isthen measured by analyser 26 at point CI.

The mixture is illuminated in photoreactor 17 for a second selectedperiod under selected and known temperature and illumination conditions.After illumination the mixture is permitted to react for a thirdselected period in reactor 29. A second nitric oxide concentration ofthe mixture is measured after the third selected period at point CII byanalyser 26. Preferably the duration of the first period is equal to thetotal duration of the second and third periods. The rate coefficient isthen calculated by computer 28 from the first and second nitric oxideconcentrations, ^(I) χ_(NO) and ^(III) χ_(NO) respectively, the knowntemperature (T) and illumination conditions (I) and the duration of thesecond selected period (^(II) t) and where the rate of smog formation isdefined as the consumption of nitric oxide per unit time by reaction(2):

    RO.sub.2 +NO→NO.sub.2                               (2)

where NO₂ denotes predominantly nitrogen dioxide but also organicnitrates and other trace nitrogenous products.

Firstly the rate of smog formation (^(T),I Q_(smog) ^(t)) inphotoreactor 17 is calculated according to equation (36)and correctedfor dilution of =[([I_(x) air by mixing with added nitric oxide by theexpression:

    .sup.T,I Q.sub.smog.sup.t =[([.sup.I χ.sub.NO -.sup.III χ.sub.NO ]/.sup.II t) (v.sub.12 +v.sub.15)/v.sub.12 ]              (50)

where v₁₂ and v₁₅ are the volumes of gas injected during specified timeby injectors 12 and 15 respectively and when v₁₂ >>v₁₅ the term (v₁₂+v₁₅)/v₁₂ can be approximated by the value 1 and where for acontinuously flowing system and continuously well mixed photoreactor 17,residence time in the photoreactor 17 (^(II) t) is given by

    .sup.II t=v.sub.17 /f.sub.17                               (51)

where v₁₇ is the volume of photoreactor 17 and f₁₇ is the volumetricflowrate of mixture through photoreactor 17.

The rate coefficient R_(smog) ^(t) is then calculated from the knownillumination and temperature conditions of photoreactor 17 and the valueof ^(T),I Q_(smog) ^(t) by application off equation (38):

    R.sub.smog.sup.t =.sup.T,I Q.sub.smog.sup.t /I.sup.t f(T.sup.t)(38)

and equation (39):

    f(T.sup.t)=e.sup.-1000γ(1/T.spsp.t.sup.-1/316)       (39)

where γ has a value of 4.7 and T,^(t) the temperature of photoreactor17, is in degrees Kelvin and I^(t) is the illumination intensity withinphotoreactor 17.

Referring to FIG. 2 a system 50 for determining concentration of smog inair includes an air filter 51 which filters incoming air and a metereddelivery injector 52 which delivers a metered dose of the filtered airto combiner 53. A metered dosage of excess nitric oxide is combined withthe filtered air in combiner 53 via nitric oxide filter 54 and metereddelivery injector 55. As a result an excess nitric oxide/air mixture isformed in combiner 53.

The concentration of nitric oxide at injector 55 is typically high sothat the volume of nitric oxide required to produce an excess nitricoxide/air mixture is small compared to the volume of the air with whichit is combined, thus optionally enabling the volume of the nitric oxideadded to be neglected for computational purposes.

Reactor 56 in which the mixture can react for a selected period whereinthe excess nitric oxide reacts with substantially all ozone in themixture is operatively coupled to combiner 53. Nitric oxide analyser 57is operatively coupled to reactor 56 to determine the nitric oxideconcentration of the mixture at point BI. Analyser 57 is alsooperatively coupled to reactor 56 via converter 58 which converts allthe NO_(y) in the mixture to nitric oxide so that the NO_(y)concentration of the mixture can be determined as nitric oxide at pointBII. The mixture is vented from the system via analyser 57 and vent 58.Computer 59 is operatively coupled to analyser 57 to calculate the smogconcentration from the NO_(y) and nitric oxide concentrations.

The concentration of smog in air can be determined in the followingmanner. A metered amount of air is delivered to combiner 53 afterpassing through filter 51 and injector 52. Excess nitric oxide is addedto the air in combiner 53 after passing through filter 54, and injector55 to provide an excess nitric oxide/air mixture in combiner 53.

The mixture is transferred to reactor 56 where it is permitted to reactfor a selected period wherein excess nitric oxide in the mixture reactswith substantially all ozone in the mixture. The nitric oxideconcentration of the mixture is then measured by analyser 57 at pointBI. The NO_(y) concentration of the mixture is then measured as nitricoxide after passing through converter 58 at point BII. The concentrationof smog is then calculated by computer 59 from the NO_(y) and nitricoxide concentrations.

The concentration of smog is the gross concentration of nitric oxideconsumed via reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)

some nitric oxide thus consumed can be regenerated by reaction (3):##STR4## however, addition of excess nitric oxide to air enablesreactions to take place in reactor 56 such that nitric oxide previouslyregenerated by (3) is consumed by reaction (4):

    NO+O.sub.3 →NO.sub.2                                (4)

The concentration of smog (χ_(smog) ^(t)) is calculated by equation (52)which is equation (16), corrected for dilution of air by mixing withadded nitric oxide:

    χ.sub.smog.sup.t =[(.sup.I χ.sub.NO.sbsb.y -.sup.I χ.sub.NO)(v.sub.52 +v.sub.55)/v.sub.52 ]              (52)

where ^(I) χ_(NO).sbsb.y is the concentration of nitric oxide at BII andI ^(I) χ_(NO) is the concentration of nitric oxide at BI and v₅₂ and v₅₅are the volumes of gas injected in specified time by injectors 52 and 55respectively.

Referring to FIG. 3 a system 70 for determining rate of smog formationin air under selected temperature and illumination conditions and ROCconcentration of air and total concentration of prior ROC emissions intoair includes an air filter 71 which filters incoming air and a metereddelivery injector 72 which delivers a metered dose of the filtered airto combiner 73, A metered dosage of excess nitric oxide is combined withthe filtered air in combiner 73 after passing through nitric oxidefilter 74 and being injected into combiner 73 by metered deliveryinjector 75. The mixture is then dispensed via two separate streams.

The concentration of nitric oxide at injector 75 is typically high sothat the volume of nitric oxide required to produce an excess nitricoxide/air mixture is small compared to the volume of the air with whichit is combined, thus enabling the volume of the nitric oxide added to beneglected for computational purposes.

Reactor 75 in which the mixture can react for a first selected periodwherein excess nitric oxide in the mixture reacts substantially allozone in the mixture is operatively coupled to combiner 73.

Photoreactor 77 is also operatively coupled to combiner 73. Illuminationsource 78 is operatively disposed about photoreactor 77 to illuminatethe mixture in photoreactor 77 for a second selected period underselected temperature and illumination conditions. Illumination fromsource 78 can be kept constant or can be varied according to apreselected or selected illumination profile. Illuminationcontroller/programmer 79 is operatively coupled to source 78 and anillumination sensor consisting of photodiode 81 and photometer 80 forthis latter purpose.

Temperature sensor 82 is operatively coupled to photoreactor 77 andtemperature controller/programmer 83 to determine the temperature of themixture in photoreactor 77. The temperature of the mixture inphotoreactor 77 can be kept constant during illumination or can beallowed to vary and monitored or can be varied according to apreselected or selected temperature profile by temperaturecontroller/programmer 83 which is operatively coupled to photoreactor 77via lines 84 and 85. Reactor 89 in which during the third selectedperiod excess nitric oxide of the mixture reacts with substantially allozone is operatively coupled to photoreactor 77.

Nitric oxide analyser 86 is operatively coupled to reactor 76 todetermine a first nitric oxide concentration of the mixture after thefirst selected period at point CI and operatively coupled to reactor 89to determine a second nitric oxide concentration of the mixture afterthe third selected period at point CII. The mixture is vented from thesystem via analyser 86 and vent 87.

Preferably reactor 76 is of the same form and volume as the combinationof the reaction vessels of photoreactor 77 and reactor 89 and theresidence time for the mixture to pass from combiner 73 to CI is thesame as that for the other part of the mixture to pass from combiner 73to CII.

Computer 88 is operatively coupled to analyser 86 to calculate the ratefrom the first and second nitric oxide concentrations and the durationof the second selected period and the ROC concentration of air and totalconcentration of prior ROC emissions into air from the first and secondnitric oxide concentration.

The rate of smog formation in air can be determined in the followingmanner. A metered amount of air is delivered to combiner 73 afterpassing through filter 71, and injector 72. Excess nitric oxide is addedto the air in combiner 73 after passing through filter 74, and injector75 to provide an excess nitric oxide/air mixture in combiner 73. Themixture is transferred to reactor 76 and photoreactor 77. The mixture ispermitted to react in reactor 76 for a first selected period whereinexcess nitric oxide in the mixture reacts with substantially all ozonein the mixture. A first nitric oxide concentration of the mixture isthen measured by analyser 86 at point CI. The mixture is illuminated inphotoreactor 77 for a second selected period under selected temperatureand illumination conditions and further allowed to react for a thirdselected period in reactor 89. A second nitric oxide concentration ofthe mixture is measured after the third selected period at point CII byanalyser 86. Preferably the duration of the first period is equal to thetotal duration of the second and third periods.

The rate ^(T),I Q_(smog) ^(t) under selected temperature andillumination conditions is then calculated by computer 88 from the firstand second nitric oxide concentrations (^(I) χ_(NO) and ^(III) χ_(NO)respectively) and the duration of the second selected period (^(II) t).

The rate of smog formation is measured as the rate of reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)

where NO₂ denotes predominantly nitrogen dioxide but also organicnitrates and other trace nitrogenous products. The rate is calculatedfrom the consumption of nitric oxide in photoreactor 77 when excessnitric oxide is present in air by utilizing equation (36) and explicitlyby the expression:

    .sup.T,I Q.sub.smog.sup.t =[({.sup.I χ.sub.NO -.sup.III χ.sub.NO }/.sup.II t) (v.sub.72 +v.sub.75)/v.sub.72 ]              (53)

where for a continuously flowing system and continuously well mixedphotoreactor 77 residence time in photoreactor 77 is given by:

    .sup.II t=v.sub.yy /f.sub.77                               (54)

where v₇₇ is the ,volume of the photoreactor 77 and f₇₇ is the flowrateof mixture through photoreactor 77 and v₇₂ and v₇₅ are the volumes ofgas injected per specified time by injectors 72 and 75 respectively.

ROC concentration of air and total concentration of prior ROC emissionsinto air can be determined in the following manner. A metered amount ofair is delivered to combiner 73 after passing through filter 71, andinjector 72. Excess nitric oxide is added to the air in combiner 73after passing through filter 74, and injector 75 to provide an excessnitric oxide/air mixture in combiner 73. The mixture is transferred toreactor 76 and photoreactor 77. The mixture is permitted to react inreactor 76 for a first selected period wherein excess nitric oxide inthe mixture reacts with substantially all ozone in the mixture. A firstnitric oxide concentration of the mixture is then measured by analyser86 at point CI. The mixture is illuminated in photoreactor 77 for asecond selected period under selected temperature and illuminationconditions and further allowed to react for a third selected period inreactor 89. A second nitric oxide concentration of the mixture ismeasured after the third selected period at point CII by analyser 86.Preferably the duration of the first period is equal to the totalduration of the second and third periods. A metered amount of referenceair of known ROC concentration and ROC composition representative ofthat of the air for analysis is delivered to combiner 73 after passingthrough filter 71, and injector 72. Excess nitric oxide is added to thereference air in combiner 73 after passing through filter 74, andinjector 75 to provide an excess nitric oxide reference air mixture incombiner 73. The reference mixture is transferred to reactor 76 andphotoreactor 77. The reference mixture is permitted to react in reactor76 for a first selected period wherein excess nitric oxide in thereference mixture reacts with substantially all ozone in the referencemixture. A first nitric oxide concentration of the reference mixture isthen measured by analyser 86 at point CI. The reference mixture isilluminated in photoreactor 77 for a second selected period underselected temperature and illumination conditions and further allowed toreact for a third selected period in reactor 89. A second nitric oxideconcentration of the reference mixture is measured after the thirdselected period at point CII by analyser 86. The duration of the first,second and third periods and selected temperature and illuminationconditions of photoreactor 77 are maintained the same during passage ofboth the air and the reference air through system 70.

The ROC concentration of the air (χ_(ROC) ^(t)) and the totalconcentration of prior ROC emissions (^(o) χ_(ROC) ^(t)) into the air iscalculated by computer 88 from the first and second nitric oxideconcentrations of the air mixture (^(I) χ_(NO) and ^(III) χ_(NO)respectively) and the first and second nitric oxide concentrations ofthe reference air mixture (^(I) χ_(NO).sup.Γ and ^(III) χ_(NO).sup.Γrespectively) and the ROC concentration of the reference air(χ_(ROC).sup.Γ).

In the presence of excess nitric oxide, nitric oxide is consumed inphotoreactor 77 in proportion to the ROC concentration of the air withinthe reactor. The ROC concentration of air is calculated from the nitricoxide consumed by the air compared to the nitric oxide consumed underthe same conditions by reference air of known ROC concentration byequation (128).

    χ.sub.ROC.sup.t =χ.sub.ROC.sup.Γ (.sup.I χ.sub.NO -.sup.III χ.sub.NO)/ (.sup.I χ.sub.NO.sup.Γ -.sup.III χ.sub.NO.sup.Γ)                                 (128)

The products of reaction by ROC species are also ROC species and for ROCcompositions representative of urban air product ROC have similarphotochemical reactivity to the reactant ROC, at least to a goodapproximation for the extent of reaction as can occur in the atmosphereon a sunny day. As the reactivity of prior ROC emissions is conservedthe total concentration of prior ROC emissions is given by

    .sup.o χ.sub.ROC.sup.t =χ.sub.ROC.sup.t            (106)

Referring to FIG. 4 a system 100 for determining rate coefficient ofsmog formation, smog concentration, amount of prior smog formation,maximum potential smog concentration, extent of smog formation in air,rate of smog formation under selected temperature and illuminationconditions, NO_(y) ozone and nitric oxide concentrations of air, timeperiod required for maximum smog formation in air under selectedconditions of temperature and illumination, ROC content of air, totalconcentration of ROC previously introduced into air, total concentrationof NO_(y) previously introduced into air, total concentration of nitricoxide previously introduced into air, NO/NO_(x) concentration ratio ofthe NO_(x) previously introduced into air, ROC/NO_(x) concentrationratio of total ROC and total NO_(x) previously introduced into air, timeperiod during which smog formation has occurred, average time ofprevious introductions of ROC into the air and time period required forproduction of selected amount of smog in air under selected conditionsof temperature and illumination, includes an air filter 101 whichfilters incoming air and a metered delivery injector 102 which deliversa metered dose of the filtered air to combiner 103 and a second metereddose to AI and NO_(y) converter 120. A metered dosage of excess nitricoxide is combined with the Filtered air in combiner 103 after passingthrough nitric oxide filter 104 and being injected therein by metereddelivery injector 105. As a result an excess nitric oxide/air mixture isformed in combiner 103 and dispensed therefrom via three separatestreams.

Reactor 106 in which the mixture can react for a First selected periodwherein excess nitric oxide in the mixture reacts with substantially allozone in the mixture, is operatively coupled to combiner 103 and reactor106A. Photoreactor 107 is also operatively coupled to combiner 103.Illumination source 108 is operatively disposed about photoreactor 107to illuminate the mixture in photoreactor 107 for a second selectedperiod under known temperature and illumination conditions. Illuminationfrom source 108 can be kept constant or can be varied according to apreselected or selected illumination profile. Illuminationcontroller/programmer 110 is operatively coupled to source 108 and anillumination sensor consisting of photodiode 111 and photometer 109 forthis latter purpose.

The illumination intensity can be determined via absolute measurement ofthe illumination intensity by sensor 111 and photometer 109 oralternatively by calibration. Calibration of the illumination intensitymay be achieved by providing a supply of air of known rate coefficientof smog formation to filter 101, the residence time of the knownair/nitric oxide mixture in photoreactor 107, the temperature ofphotoreactor and the nitric oxide concentrations at CI and CII.

Temperature sensor 112 is operatively coupled to photoreactor 107 andtemperature controller/programmer 113 to determine the temperature ofthe mixture in photoreactor 107. The temperature of the mixturephotoreactor 107 can be kept constant during illumination or can beallowed to vary and monitored or can be varied according to apreselected or selected temperature profile by temperaturecontroller/programmer 113 which is operatively coupled to photoreactor107 via lines 114 and 115.

Reactor 106 in which during a third selected period excess nitric oxidereacts with substantially all ozone in the mixture is operativelycoupled to photoreactor 107.

Nitric oxide analyser 117 is operatively coupled to reactor 106A todetermine a first nitric oxide concentration of the mixture after thefirst selected period at point CI and operatively coupled to reactor 116to determine a second nitric oxide concentration of the mixture afterthe third selected period at point CII.

Reactors 106 and 106A have form and configuration similar to thecombined assembly of photoreactor 107 and reactor 116, respectively, bywhich means the mixing processes and the residence time of that part ofthe mixture passing from combiner 103 to point CI is approximately thesame as that part of the mixture passing from combiner 103 to point CII,thus ensuring that the mixture composition at any moment at CI and atCII pertain to air which initially formed part of a common mixturecombiner 103. This feature is particularly useful when the compositionof air passing through filter 101 is variable.

Reactor 118 in which mixture can react for a fourth selected periodwherein excess nitric oxide of the mixture reacts with substantially allozone in the mixture is operatively coupled to combiner 103. Analyser117 is operatively coupled to reactor 118 to determine nitric oxideconcentration of the mixture at point BI. Analyser 117 is alsooperatively coupled to reactor 118 via NO_(y) converter 119 to determinea NO_(y) concentration of the mixture at point BII. Analyser 117 is alsooperatively coupled to injector 102 to determine the nitric oxideconcentration of the air at point AI. Analyser 117 is also operativelycoupled to injector 102 via NO_(y) converter 120 to determine the NO_(y)concentration of the air at point AII. The mixture and air are ventedfrom the system via analyser 117 and vent 121. Computer 122 isoperatively coupled to temperature sensor 112, photometer 109, analyser117. Computer 122 is also operatively coupled to temperature sensor 123and illumination sensor 124. Temperature sensor 123 is disposed todetermine the temperature of the ambient air prior to analysis by system100 and illumination sensor 124 is disposed to determine the sunlightflux in the ambient air.

Optionally, a nitric acid scrubber 125 is coupled to the inlet atconverter 120 and a nitric acid scrubber 126 is coupled to the inlet ofconverter 119 to remove nitric acid vapour from the air and mixturerespectively prior to entering the converters 119 and 120.

Computer 122 processes signals from operatively coupled to sensors andanalyser to calculate: the rate coefficient of smog formation in airfrom the nitric oxide concentrations at CI and CII, the knowntemperature and illumination conditions of photoreactor 107 and theduration of the second selected period; the concentration of smog in airfrom the nitric oxide concentrations at BI and BII; the amount of priorsmog formation from concentrations of nitric oxide at AII, 8I and BII;the maximum potential smog concentration of air from the nitric oxideconcentrations measured at AII, BI and BII; extent of smog formation inair from the concentrations of nitric oxide measured at AII, BI and BII;the rate of smog formation under the selected conditions of temperatureand illumination from the nitric oxide concentrations measured at CI andCII and the duration of the second selected period; the NO_(y)concentration of air from the nitric oxide concentration measured atAII; the ozone concentration of air from the nitric oxide concentrationsmeasured at AI, BI and BII and the nitric oxide concentration of airfrom the nitric oxide concentration measured at AI and (oralternatively) the ozone and nitric oxide concentrations of air from themeasured nitric oxide concentrations at AII, BI and BII and thetemperature of air as measured at sensor 123 and illumination intensityof sunlight at sensor 124; the time period required for maximum smogformation in air under selected conditions of illumination andtemperature from the measured nitric oxide concentrations at AII, BI,BII, CI and CII, and the duration of the second selected period; timeperiod during which smog formation in air has occurred, the time periodbeing substantially the same as or within a selected period for whichthe illumination and temperature conditions are known, wherein the endof the selected period coincides with the end of the time period fromthe measured nitric oxide concentrations at AII, BI, BII, CI, CII, theduration of the second selected period, the temperature measured atsensor 112 and illumination intensity measured at sensor 111 and thetemperature and illumination of air monitored by sensors 123 and 124respectively throughout the duration of the selected period during whichsmog formation in air has occurred; time period required for productionof selected amount of smog in air under selected conditions oftemperature and illumination from the nitric oxide concentrationsmeasured at AII, BI, BII, CI and CII, the duration of the secondselected period, the temperature measured at sensor 112 and theillumination intensity measured at sensor III and the selectedconditions of temperature and illumination of the air and the selectedamount of smog; the ROC content of air from the nitric oxideconcentrations at CI and CII, the temperature measured at sensor 112 andillumination intensity measured at sensor 111 and the duration of thesecond selected period; the total concentration of ROC previouslyintroduced into air from the ROC content of air determined as above; theNO_(y) concentration of air from the nitric oxide concentration measuredat AII; the total concentrations of NO_(x) and NO_(y) previouslyintroduced into air from the nitric oxide concentrations measured at AI,AII, BI and BII or alternatively from the measured nitric oxideconcentrations measured at AII, BI and BII, the temperature of the airmeasured at sensor 123 and illumination intensity of sunlight measuredat sensor 124; the total concentration of nitric oxide previouslyintroduced into air from the nitric oxide concentrations measured at AI,AII, BI and BII or alternatively from the nitric oxide concentrationsmeasured at AII, BI and BII, the temperature of the air measured atsensor 123 and illumination intensity of sunlight measured at sensor124; the NO/NO_(x) concentration ratio of the NO_(x) introduced into air(^(o) F_(NO)) from the NO concentrations measured at AI, AII, BI andBII, the temperature of the air measured at sensor 123 and theillumination intensity of sunlight measured at sensor 124; theROC/NO_(x) concentration ratio of the total ROC and total NO_(x)previously introduced into air from the nitric oxide concentrationsmeasured at AII, BI, BII, CI and CII, the temperature measured at sensor112 and illumination intensity measured at sensor 111, the duration ofthe second selected period and also the NO concentration measured at AIor alternatively the temperature of the air measured at temperaturesensor 123 and illumination intensity of sunlight measured at sensor124; average time of prior introductions of ROC into air from theconcentrations of nitric oxide at AII, BI, BII, CI and CII, thetemperature-time profile of the air measured at temperature sensor 123,the illumination intensity-time profile of the air measured at sunlightillumination sensor 124 and also the NO concentration measured at AI oralternatively the air temperature measured at sensor 123 at the time ofsampling the air and the illumination intensity measured at sensor 124at the time of sampling the air.

The rate coefficient of smog formation in air can be determined thefollowing manner:

A metered amount of air is delivered to combiner 103 after passingthrough filter 101 and injector 102. Excess nitric oxide is added to theair in combiner 103 after passing through filter 104 and injector 105 toprovide an excess nitric oxide/air mixture in combiner 103. Meteredamounts of the mixture are transferred to reactor 106 and 106A andphotoreactor 107. The mixture is permitted to react in reactor 106 and106A for a first selected period wherein excess nitric oxide in themixture reacts with substantially all ozone in the mixture. A firstnitric oxide concentration of the mixture is then measured by analyser117 at point CI. The mixture is illuminated in photoreactor 107 for asecond selected period under known temperature and illuminationconditions and then transferred to reactor 116. The mixture is permittedto react in reactor 116 for a third selected period wherein excessnitric oxide in the mixture reacts with substantially all ozone.

A second nitric oxide concentration of the mixture is measured after thethird selected period at point CII by analyser 117. The rate coefficientis then calculated by computer 122 from the first and second nitricoxide concentrations, the known temperature and illumination conditionsof photoreactor 107 and the duration of the second selected period.

In system 100 optionally reactors 106 and 106A and reactor 118 are thesame reactor and then points BI and CI become the same point, howeverthere is an advantage in employing separate reactors of differingvolumes as reactors 106 and 106A and reactor 118. This is becausepreferably the residence time of the mixture in reactors 106 and 106A isthe same as the combined residence times of mixture in reactors 107 and116, and the residence time in photoreactor 107 is preferred to be inthe order of ten minutes, the longer the residence time in photoreactor107 the greater being the sensitivity of system 100 for determining rateof smog formation and rate coefficient of smog formation. The residencetime preferred for the mixture in reactor 118 is shorter than thepreferred residence time in photoreactor 107 and is of the order of oneminute and it is preferred that the residence time of the mixture inreactor 118 is as short as is consistent with the reaction of ozone withexcess nitric oxide going substantially to completion in reactor 118.This is desirable especially when the composition of air at filter 101is rapidly varying for then the air delivered from filter 101 toanalyser 117 via points AI and AII will be close to having the samecomposition as air delivered from filter 101 to analyser 117 via pointsBI and BII. This in turn minimizes the possibility of transitoryspurious values for ozone concentrations being determined by system 100due to the mixture measured at points A and B having as origins air ofdifferent compositions

The rate coefficient for smog formation in air is determined bymeasurement of nitric oxide consumed by reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)

in photoreactor 107. Some nitrogen dioxide produced by reaction (2)undergoes further reaction in photoreactor 107, producing ozone andregenerating nitric oxide by reaction (3): ##STR5## Nitric oxideregenerated by reaction (3) further reacts with excess nitric oxide byreaction (4):

    NO+O.sub.3 →NO.sub.2                                (4)

either within photoreactor 107 or subsequently in reactor 116. Thenitric oxide consumed by photoreaction of ROE species in photoreactor107 is the difference in nitric oxide concentrations of the mixture atpoints CII and CI. The rate of smog formation (^(T),I Q_(smog) ^(t)) inphotoreactor 107 is calculated by equation (36), corrected for dilutionof air by mixing with added nitric oxide, by the expression:

    .sup.T,I Q.sub.smog.sup.t ={[(.sup.I χ.sub.NO -.sup.III χ.sub.NO)/.sup.II t][(v.sub.102 +v.sub.105)/v.sub.102 ]}(55)

where ^(III) χ_(NO) is the concentration of nitric oxide measured at CIIand ^(I) χ_(NO) is the nitric oxide concentration measured at CI byanalyser 117 and where v₁₀₂ and v₁₀₅ are the volumes of gas injectedduring specified time into combiner 103, by injectors 102 and 105respectively. Optionally where V₁₀₂ >>V₁₀₅ the term (v₁₀₂ +v₁₀₅)/v₁₀₂can be approximated by the value 1 and where for a continual flowthroughsystem 100 and continuously well mixed photoreactor 107, residence timein the photoreactor 107 (^(II) t) is given by:

    .sup.II t=v.sub.107 /f.sub.107                             (56)

where v₁₀₇ is the volume of photoreactor 107, and f₁₀₇ is the volumetricflowrate of mixture supplied by combiner 103 and passing throughphotoreactor 107.

The rate coefficient R_(smog) ^(t) is calculated from the knownillumination and temperature conditions of photoreactor 107 and thevalue of 2 Q_(smog) ^(t) by application of equation (38):

    R.sub.smog.sup.t .sup.T,I Q.sub.smog.sup.t /I.sup.t f(T.sup.t)(38)

and equation (39):

    f(T.sup.t)=e.sup.-1000γ(1/T.spsp.t.sup.-1/316)       (39)

where γ has a value of 4.7 and the temperature of photoreactor 107(T^(t)) is in degrees Kelvin and I^(t) is the illumination intensitywithin photoreactor 107.

The concentration of smog in air can be determined in the followingmanner.

A metered volume of air is delivered to combiner 1033 after passingthrough filter 101 and injector 102. Metered volume of excess nitricoxide is added to the air in combiner 103 after passing through filter104 and injector 105 to provide an excess nitric oxide/air mixture incombiner 103. The mixture is transferred to reactor 118. The mixturepermitted to react in reactor 118 for a fourth selected period whereinexcess nitric oxide in the mixture reacts with substantially all ozonein the mixture. A third nitric oxide concentration of the mixture isthen measured by analyser 117 at point BI. Mixture from reactor 318 isdelivered to nitric oxide converter 119 wherein the NO_(y) in themixture is converted to nitric oxide. The mixture is delivered fromconverter 119 to point BII and a fourth nitric oxide concentrationmeasured by analyser 117. The concentration of smog in air is thencalculated by computer 122 from the third and fourth nitric oxideconcentrations.

As already indicated, smog concentration of air is the sum of theconcentrations of ozone and NO_(y) less the concentration of NO, andχ_(smog) ^(t) is the concentration of smog in air at time t. It followsthat χ_(smog) ^(t) is equivalent to the concentration of nitrogendioxide and other gas phase nitrogen containing species in air producedby reaction of nitrogen dioxide, that is, the nitrogenous products offreactions (3) and (6): ##STR6## When excess nitric oxide is added toair, nitrogen dioxide consumed by reaction (3) is regenerated from theozone produced by reaction (3) by reaction (4):

    NO+O.sub.3 →NO.sub.2                                (4)

enabling the smog concentration of air (χ_(smog) ^(t)) to be calculatedfrom the difference in nitric oxide concentrations at points BII and BI,by equation (57):

    χ.sub.smog.sup.t =[(.sup.BII χ.sub.NO -.sup.BI χ.sub.NO) (v.sub.102 +v.sub.105)/v.sub.102 ]                        (57)

where ^(BII) χ_(NO) and ^(BI) χ_(NO) are the concentrations of nitricoxide at points BII and BI respectively and measured by analyser 117 andv₁₀₂ and v₁₀₅ are the volumes of gas injected during specified time intocombiner 103 by injectors 102 and 105 respectively.

The rate of smog formation in air under selected temperature andillumination conditions can be determined in the following manner:

A metered amount of air is delivered to combiner 103 after passingthrough filter 101 and injector 102. Excess nitric oxide is added to theair in combiner 103 after passing through filter 104 and injector 105 toprovide an excess nitric oxide/air mixture in combiner 103. Meteredamounts of the mixture are transferred to reactors 106 and 106A andphotoreactor 107. The mixture is permitted to react in reactors 106 and106A for a first selected period wherein excess nitric oxide in themixture reacts with substantially all ozone in the mixture. A firstnitric oxide concentration of the mixture is then measured by analyser117 at point CI. The mixture is illuminated in photoreactor 107 for asecond selected period under the selected temperature and illuminationconditions and then transferred to reactor 116. The mixture is permittedto react in reactor 116 for a third selected period wherein excessnitric oxide in the mixture reacts with substantially all ozone.

The rate of smog formation in air under the selected temperature andillumination conditions of photoreactor 107 is the rate of reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)

Some nitrogen dioxide produced by reaction (2) undergoes furtherreaction in photoreactor 107, producing ozone and regenerating nitricoxide according to reaction (3): ##STR7## Nitric oxide regenerated byreaction (3) further reacts with excess nitric oxide according toreaction (4):

    NO+O.sub.3 →NO.sub.2                                (4)

either within photoreactor 107 or subsequently in reactor 116. Thus, theamount of nitric oxide consumed by reaction (2) in photoreactor 107 isequal to The difference in nitric oxide concentrations of the mixturebetween points CII and CI. The rate of smog formation (^(T),I Q_(smog)^(t)) under the selected conditions of illumination I and temperature Tof photoreactor 107 is calculated according to equation (36) andcorrected for dilution of air by mixing with added nitric oxide,according to the expression:

    .sup.T,I Q.sub.smog.sup.t ={[(.sup.I χ.sub.NO -.sup.III χ.sub.NO)/.sup.II t][(v.sub.102 +v.sub.105)/v.sub.102 ]}(55)

where ^(III) χ_(NO) is the concentration of nitric oxide measured at CIIand ^(I) χ_(NO) is the nitric oxide concentration measured at CI byanalyser 117 and where v₁₀₂ and v₁₀₅ are the volumes of gas injectedduring the specified time into combiner 103, by injectors 102 and 105respectively. Optionally where v₁₀₂ >>v₁₀₅ the expression (v₁₀₂+v₁₀₅)/v₁₀₂ can be approximated by the value 1. For a continuallyflowing system and continuously well mixed photoreactor 107, residencetime in the photoreactor 107 (^(II) t) is given by:

    .sup.II t=v.sub.107 /f.sub.107                             (56)

where v₁₀₇ is the volume of photoreactor 107, and f₁₀₇ is the volumetricflowrate of mixture supplied by combiner 103 and passing throughphotoreactor 107.

The NO_(y), nitric oxide and ozone concentrations of air can bedetermined in the following manner. Air from injector 102 is deliveredto nitric oxide converter 120 wherein all the NO_(y) in the air isconverted to NO. The mixture from converter 120 is delivered to pointAII and the NO_(y) concentration of the air is measured as a fifthnitric oxide concentration ^(AII) χ_(NO) at point AII and theconcentration of NO_(y) calculated according to equation (89):

    χ.sub.NO.sbsb.y.sup.t =.sup.AII χ.sub.NO.sup.t     (89)

Air from injector 102 is delivered to point AI and the nitric oxideconcentration of air is measured as a sixth nitric oxide concentration(^(AI) χ_(NO)) by analyser 117 at point AI and the concentration ofnitric oxide in air calculated according to equation (63):

    χ.sub.NO.sup.t =.sup.AI χ.sub.NO.sup.t             (63)

The ozone concentration of air χ_(smog) ^(t) is calculated by computer122 from the fifth and sixth nitric oxide concentrations and the smogconcentration of air χ_(smog) ^(t) according to equation (44) byequation (62):

    χ.sub.O.sbsb.3.sup.t ≦χ.sub.smog.sup.t +.sup.AI χ.sub.NO.sup.t -.sup.AII χ.sub.NO.sup.t           (62)

The amount of prior smog formation in air (^(f) χ_(smog) ^(t)) can bedetermined in the following manner. The smog concentration of air(χ_(smog) ^(t)) is determined as described and calculated according toequation (57) and also air from injector 102 is delivered to converter120 wherein all NO_(y) of the air is converted to nitric oxide. TheNO_(y) concentration of the air (χ_(NO).sbsb.y^(t)) is then measured asa fifth nitric oxide concentration by analyser 117 at point AII (^(AII)χ_(NO) ^(t)). The concentration at time t of NO_(y) that would exist inthe absence of NO_(y) removal processes from air (^(o)χ_(NO).sbsb.y^(t)), and which represents the cumulative emissions ofNO_(y) into air is calculated from the values determined forχ_(NO).sbsb.y^(t), χ_(NO) ^(t) and χ_(O).sbsb.3^(t).

The procedure for determining ^(o) χ_(NO).sbsb.y^(t) depends on theextent of smog formation E_(smog) ^(t) <1 then the NO_(y) (E_(smog) ^(t)equation 34,when) lost from the air by the action of reaction (7) can beevaluated on the basis of the measured values of χ_(NO).sbsb.y^(t),χ_(NO) ^(t) and χ_(O).sbsb.3^(t) and the values of P₇,2 and ^(o) F_(NO).When E_(smog) ^(t) =1 smog formation does not occur in the air (becauseof insufficient concentration of nitric oxide to enable reaction (2) toproceed at an appreciable rate) but NO_(y) can continue to be removedfrom the air via reaction (7). In the case of E_(smog) ^(t) =1 anothermethod is used to evaluate ^(o) χ_(NO).sbsb.y^(t) which employs thevalue measured for χ_(O).sbsb.3^(t) and which is independent ofχ_(NO).sbsb.y^(t).

To determine the domain of E_(smog) ^(t) the value of G^(t) isdetermined according to equation (58). ##EQU3##

The denominator of equation (58) is an expression for ^(o)χ_(NO).sbsb.y^(t) according to equation (59) which is derived fromequations (19, 21 and 27) and which is appropriate to the case ofE_(smog) ^(t) <1 but which underestimates the value of ^(o)χ_(NO).sbsb.y^(t) when E_(smog) ^(t) =1.

The numerator of equation (58) is an expression for ^(o)χ_(NO).sbsb.y^(t) according to equation (60) which is appropriate to thecase of E_(smog) ^(t) =1 but which underestimates the value of ^(o)χ_(NO).sbsb.y^(t) when E_(smog) ^(t) <2.

    When

    G.sup.t =1

    then

    E.sub.smog.sup.t <1

    and when

    G.sup.t ≮1

    then

    E.sub.smog.sup.t =1                                        (129)

and

    .sup.o χ.sub.NO.sbsb.y.sup.t =χ.sub.NO.sbsb.y.sup.t +P.sub.7,2 (.sup.o F.sub.NO χ.sub.NO.sbsb.y.sup.t +χ.sub.O.sbsb.3.sup.t -χ.sub.NO.sup.t)/(1-.sup.o F.sub.NO P.sub.7,2 (E.sub.smog.sup.t <1)(59)

otherwise

    .sup.o χ.sub.NO.sbsb.y.sup.t =χ.sub.O.sub.3.sup.t /(β-.sup.o F.sub.NO) (E.sub.smog.sup.t =1)                           (60)

Equation (60) arises from the following considerations:

When E_(smog) ^(t) then the value of χ_(NO) ^(t) is small andapproaching zero, thus for the purpose of these calculations nitricoxide concentration can be assigned the value

    χ.sub.NO.sup.t =O (E.sub.smog.sup.t =1)

    Also when

    E.sub.smog.sup.t =1

    then .sup.r χ.sub.smog.sup.t =.sup.fmax χ.sub.smog.sup.t

    and by equation (31)

    .sup.f χ.sub.smog.sup.t =β.sup.o χ.sub.NO.sbsb.y.sup.t (E.sub.smog.sup.t =1)                                     (120)

Now for the case E_(smog) ^(t) =1 (and χ_(NO) ^(t) =0) it follows from tequations (17), (18) and (27) that the ozone concentration of air isgiven by

    χ.sub.O.sbsb.3.sup.t =.sup.Tmax χ.sub.smog.sup.t -.sup.o F.sub.NO.sup.o χ.sub.NO.sub.y.sup.t (E.sub.smog.sup.t =1)(122)

Substitution of (118) into (122) gives ^(o) χ_(NO).sbsb.y^(t) in termsof χ_(O).sbsb.3^(t)

    χ.sub.O.sbsb.3.sup.t =.sup.o χ.sub.NO.sbsb.y.sup.t (β-.sup.o F.sub.NO) (E.sub.smog.sup.t =1)                           (123)

and (123) can be rearranged to make ^(o) χ_(NO).sbsb.y^(t) the dependentvariable, yielding equation (60).

The amount of prior smog formation in air is calculated according toequations (29), (31), (57), (58) and (62) by equation (61):

    .sup.f χ.sub.smog.sup.t ={[χ.sub.smog.sup.t -(1-.sup.o F.sub.NO).sup.AII χ.sub.NO.sup.t ]/ (1-.sup.o F.sub.NO P.sub.7,2)}G.sup.t <1

    or

    .sup.f χ.sub.smog.sup.t =βχ.sub.O.sbsb.3.sup.t /(β-.sup.o F.sub.NO) T.sup.t ≮1                          (61)

where β, ^(o) F_(NO) and P₇,2 are independently determined coefficientswhich for most circumstances pertinent to air of composition as commonlyfound in urban regions can be assigned the values:

    β=4

    .sup.o F.sub.NO =0.9

    P.sub.7,2 =0.125.

The value of P₇,2 is a function of the relative rates of reactions (7)and (2). However, the rate of reaction (7) can be variable as theproduct distribution of the reaction of NO₂ with RO₂ can vary. In somecircumstances nitric acid, one of the reaction products, can remain inthe gas phase or alternatively a variable proportion of the nitric acidformed can be incorporated, possibly by adsorption, into non-gaseousspecies. The effect of this variability of product distribution on thevalue of P₇,2 may optionally be minimized by incorporation of nitricacid scrubbers 125 and 126 into the system. When scrubbers 125 and 126are included then nitric acid is excluded from the definition of NO_(y).A suitable nitric acid scrubber is a porous nylon membrane or nylon tubethrough which the sample and mixture a:-e passed. Nylon surfaces removenitric acid from air. When nitric acid is thus removed prior toconverters 120 and 121 then the relative rates of reactions (7) and (2)are made less variable but the rate of reaction (7) is increased. Whennitric acid scrubbers are incorporated into system 100 a value of aboutP₇,2 =0.25 is suitable for most determinations of prior smog formationin air.

The maximum potential smog concentration in air (^(fmax) χ_(smog) ^(t))can be calculated from the determined value of ^(o) χ_(NO).sbsb.y^(t) inair.

The extent of smog formation in air at time t (E_(smog) ^(t)), being theproportion of smog produced by time t compared to the maximum potentialamount of smog formation can be determined from ^(fmax) χ_(smog) ^(t)and ^(max) χ_(smog) ^(t) according to equations (61) and (31)respectively according to equation (35):

    E.sub.smog.sup.t =(.sup.f χ.sub.smog.sup.t /.sup.fmax χ.sub.smog.sup.t)                                     (35)

System 100 provides other methods for determination of the nitric oxideand ozone concentrations of air, which are as follows: The illuminationintensity of air is measured by sensor 124 and the temperature of air ismeasured by sensor 123.

The nitric oxide and ozone concentrations are determined by firstcalculating the rate coefficient of reaction (3) k₃ ^(t), from the knowncoefficients for NO₂ photolysis, the illumination intensity measured bysensor 124 and the temperature measured by sensor 123. If k₃ ^(t) iszero then the nitric oxide and ozone concentrations are calculated byequations (68) and (69) respectively and the values of χ_(smog) ^(t) andχ_(NO).sbsb.y^(t), obtained as described previously.

If k₃ ^(t) is non zero then the values of ^(o) χ_(NO) ^(t), ^(o)χ_(NO).sbsb.y^(t), χ_(smog) ^(t) and ^(f) χ_(smog) ^(t) are obtained asdescribed previously and the domain of ^(f) χ_(smog) ^(t) determinedaccording to expression (70). If the value of ^(f) χ_(smog) ^(t) fallsoutside the range of expression (70) then the nitric oxide and ozoneconcentrations are calculated according to equations (68) and (69)respectively. When ^(f) χ_(smog) ^(t) falls within the range specifiedby expression (70) then the rate coefficient for reaction (4) iscalculated from the known rate parameters and the temperature measuredby sensor 123. The nitric oxide and ozone concentration of air arecalculated from the values of k₃ ^(t), k₄ ^(t), χ_(smog) ^(t) andχ_(NO).sbsb.y^(t) according to equations (125) and (126) respectivelyand equation (71) by equations (73) and (74) respectively.

    χ.sub.NO.sup.t  ≦ {χ.sub.NO.sbsb.y.sup.t  - χ.sub.smog.sup.t k.sub.e.sup.t /k.sub.4.sup.t  + [(χ.sub.NO.sbsb.y.sup.t  - χ.sub.smog.sup.t  - k.sub.e.sup.t /k.sub.4.sup.t).sup.2  + 4k.sub.3.sup.t χ.sub.NO.sbsb.y.sup.t /k.sub.4.sup.t ].sup.1/2}/ 2                              (73)

    χ.sub.O.sbsb.3.sup.t  = {χ.sub.smog.sup.t  - χ.sub.NO.sbsb.y.sup.t  - k.sub.3.sup.t /k.sub.4.sup.t  + [(k.sub.e.sup.t /k.sub.r.sup.t   + χ.sub.NO.sbsb.y.sup.t  - χ.sub.smog.sup.t).sup.2  + 4k.sub.3.sup.t χ.sub.smog.sup.t /k.sub.4 ].sup.1/2 }/2                                    (74)

(Valid domain for (73) and (74) is when f.sub.χ_(smog) ^(t) is in therange

    (.sup.o χ.sub.NO.sup.t  - H.sup.o χ.sub.NO.sbsb.y.sup.t  < .sup.t χ.sub.smog.sup.t  < (.sup.o χ.sub.NO.sup.t  + L.sup.o χ.sub.NO.sbsb.y.sup.t)                                (70)

and where expression (70) may be adequately approximated by

    χ.sub.NO.sbsb.y.sup.t (.sup.o F.sub.NO `1/2)<`.sub.smog.sup.t <χ.sub.NO.sbsb.y.sup.t (.sup.o F.sub.NO +1/2)         (127)

The time period required for maximum smog formation in air subsequent tothe period of the actual smog formation under selected conditions oftemperature and illumination can be determined in the following manner:

The values of ^(o) χ_(NO).sbsb.y^(t) and ^(f) χ_(smog) ^(t) aredetermined as above described and the maximum potential smogconcentration of air calculated according to equation (31):

    .sup.fmax χ.sub.smog.sup.t =β.sup.o χ.sub.NO.sbsb.y.sup.t(31)

The amount of further smog formation required (^(extra) χ_(smog) ^(t))to produce maximum smog concentration is calculated according toequation (79):

    .sup.extra χ.sub.smog.sup.t =.sup.fmax χ.sub.smog.sup.t -.sup.f χ.sub.smog.sup.t                                      (79)

The time period (t₂ -t₁) where t₁ is the commencement and t₂ is thecompletion time to form the amount of smog equivalent to ^(extra)χ_(smog) ^(t) is determined from the rate coefficient for smog formationdetermined as described above and is calculated for the selectedtemperature and illumination conditions according to equations (39),(42) and (43) by the solution of equation (80) for (t₂ -t₁): ##EQU4##and where a suitable value for γ is 4.7.

The time period during which smog formation in air has occurred (t_(t)-t_(o)), the time period being substantially the same as or within aselected period wherein the end of the selected period coincides withthe end of the formation period, can be determined in the followingmanner. For the duration of selected period the illumination intensityof the air is measured by sensor 124 and the temperature of the air ismeasured by sensor 123. At the end of selected period (t_(t)) the ratecoefficient for smog formation in air, R_(smog) ^(t), and the amount ofsmog formation in air, ^(f) χ_(smog) ^(t), and the amount of prioremissions of NO_(y) into the air, ^(o) χ_(NO) _(y), are determined asdescribed above. The time period (t_(t) -_(o)) is calculated from thesevalues according to equations (27), (39), (42) and (43) by solution ofequation (81) for (t_(t) -t_(o)): ##EQU5## where

    .sup.T,I Q.sub.smog.sup.t =R.sub.smog.sup.t I.sup.t f(T.sup.t)

    when

    .sup.f χ.sub.smog.sup.t <β.sup.o χ.sub.NO.sbsb.y.sup.t

    or

    .sup.T,I Q.sub.smog.sup.t =0 .sup.f χ.sub.smog.sup.t ≮β.sup.o χ.sub.NO.sbsb.y.sup.t

    and

    f(T.sup.t)=e.sup.-1000γ(1/T.spsp.t.sup.-1/316)       (39)

The time period determined by equation (81) is contingent on the premisethat all the ROC of the air is present at the commencement of the timeperiod. When this is not the case the determined commencement time t_(o)is some average of the times during which ROC was introduced into theair. When condition ^(f) χ_(smog) ^(t) =β^(o) χ_(NO).sbsb.y^(t) metduring the time period then maximum potential smog formation is reachedand the time period determined is a minimum period because the maximumextent of smog formation may have existed for an indeterminate timeprior to the end of the selected period.

Optionally if the trajectory and speed of movement of the air during theselected period is known, then the time period during which smogformation has occurred can be used in conjunction with this furtherinformation to estimate the location of the source of the ROC emissions,which corresponds to the location of the air at time t=t_(o).

The time period (t_(t) to t_(m)) required for production of selectedamount of smog in air (^(select) χ_(smog)) under selected conditions oftemperature and illumination can be determined in the following manner.The values of ^(f) χ_(smog) ^(t) ^(max) χ_(smog) ^(t) and R_(smog) ^(t)are determined as above described. The selected amount of smog is testedaccording to expression (82) to determine if the smog amount selected iswithin the range of possible smog amounts:

    .sup.select χ.sub.smog ≦(.sup.max χ.sub.smog.sup.t -.sup.f χ.sub.smog.sup.t)                                     (82)

If expression (82) is false then the time required for production ofselected amount of smog is indefinite because the selected amount ismore than the amount that can be produced from the air.

When expression (82) is true then time period (t_(t) to t_(m)) iscalculated by solution of equation (83) for t_(m) : ##EQU6## where t_(t)is the time at commencement of smog formation and t_(m) is the time whenproduction of selected amount of smog in air is attained and a suitablevalue for the coefficient γ is 4.7.

The ROC content of air (χ_(ROC) ^(t)) can be determined in the followingmanner. The rate coefficient for smog formation in air R_(smog) ^(t) isdetermined as described above and the value of χ_(ROC) ^(t) calculatedaccording to equation (105)

    χ.sub.ROC.sup.t =R.sub.smog.sup.t /a.sub.ROC.sup.t     (105)

where for ROC emissions of compositions as commonly found in urbanregions a suitable value for a_(ROC) ^(t) is a_(RO) ^(t) =0.0067 molessmog/mole ROC carbon/unit illumination intensity where illuminationintensity has units of rate coefficient for NO₂ photolysis integratedwith respect to time.

Alternatively the value of a_(ROC) ^(t) can be separately determined.The value of χ_(ROC) ^(t) thus determined has units of concentration inair of carbon present as ROC.

The total concentration of ROC previously introduced into air (^(o)χ_(ROC) ^(t)) can be determined in the following manner. The ROC contentof air is determined as described above. As to a good approximation thevalue of the smog forming reactivity of air (R_(smog) ^(t)) isindependent of the amount of illumination to which the ROC/air mixturehas been exposed on the day of measurement. The value of ^(o) χ_(ROC)^(t) can be calculated according to equation (106)

    .sup.o χ.sub.ROC.sup.t =χ.sub.ROC.sup.t            (106)

The total concentration of NO_(y) previously introduced into air (^(o)χ_(NO).sbsb.y^(t)) can be determined in the following manner. The valuesof χ_(NO).sbsb.y^(t), χ_(NO) ^(t) and χ_(O).sbsb.3^(t) are determinedfor the air as described above and the value of G^(t) calculatedaccording to equation (58), when G^(t) has a value of G^(t) <1 the valueof ^(o) χ_(NO).sbsb.y^(t) is calculated from the determined values ofχ_(NO).sbsb.y^(t), χ_(NO) ^(t) and χ_(O).sbsb.3^(t) according toequation (59) and where suitable values for the coefficients P₇,2 and^(o) F_(NO) are 0.125 and 0.9 respectively or otherwise, when G^(t) ≮1,from the determined values of χ_(O).sbsb.3^(t) according to equation(60) and where a suitable value for the coefficient β is 4.

The total concentration of nitric oxide previously introduced into air(^(o) χ_(NO) ^(t)) can be determined in the following manner. The valueof ^(o) χ_(NO).sbsb.y^(t) the air is determined as described aboveFollowing equation (11) expressed in terms of concentrations the valueof ^(o) χ_(NO) ^(t) is calculated according to equation (109)

    .sup.o χ.sub.NO.sup.t =.sup.o F.sub.NO.sup.o χ.sub.NO.sbsb.y.sup.t( 109)

where in most circumstances pertaining to urban air a suitable value forthe coefficient ^(o) F_(NO) is 0.9 or alternatively the value of ^(o)F_(NO) can

The NO/NO_(x) concentration ratio of the NO_(x) introduced into air beindependently determined by measurement of the NO_(x) emissions it theirsource.

NO/NO_(x) concentration ratio of the NO_(x) introduced into air (^(o)F_(NO)) can be determined in the following manner. The concentrationsχ_(smog) ^(t), χ_(O).sbsb.3^(t), χ_(NO) ^(t) and χ_(NO).sbsb.y^(t) ofthe air are determined from the nitric oxide concentrations measured atAI, AII, BI and BII and calculated as described above according toequations (57), (62), (63) and (89) respectively. The temperature of theair at the time of sampling the air is determined by temperature sensor123 and the sunlight illumination intensity at the time of sampling theair is determined by sensor 124. The value of ^(o) F_(NO) is determinedfrom these values by solution for ^(o) F_(NO) of the set of equations(29) (58) (59) (60), (109) and (68) or (69) or (73) or (74) and wheresuitable values for the coefficients of these equations are

    P.sub.7,2 =0.125, β=4 and H=L=1/2

The ROC/NO_(x) concentration ratio Of the total ROC and total NO_(x)previously introduced into air (^(o) χ_(ROC) ^(t) /^(o) χ_(NO) ^(t)) canbe determined in the following manner. The values of ^(o) χ_(ROC) ^(t)and ^(o) χ_(NO) ^(t) are determined for the air as described above andfollowing equations (10) and (106) the ROC/NO_(x) concentration ratiocan be calculated from the determined concentrations according toequation (108)

    .sup.o χ.sub.ROC.sup.t /.sup.o χ.sub.NO.sbsb.x.sup.t =χ.sub.ROC.sup.t /.sup.o χ.sub.NO.sbsb.y.sup.t    (108)

The average time of prior introductions of ROC into air (t_(o)) can bedetermined in the following manner. The time period during which smogformation has occurred (t_(t) -t_(o)) is determined as described aboveand the average time of emission of ROC into the air calculated from thetime of air sampling (t_(t)) and the duration of the time period duringwhich smog formation has occurred according to equation (113)

    t.sub.o =t.sub.t -(t.sub.t -t.sub.o)                       (113)

Referring to FIG. 5 a system 130 for determining rate coefficient ofsmog formation in air includes an air filter 131 which filters incomingair and a metered delivery injector 132 which delivers a metered dose ofthe filtered air to a first combiner 133. A metered dosage of nitricoxide is combined with the filtered air in combiner 133 after passingthrough nitric oxide filter 134 and being injected therein by metereddelivery injector 135.

The nitric oxide/air mixture thus formed is delivered to second combiner136. A metered dosage of excess ozone is combined with the mixture incombiner 136 after passing through ozone filter 137 and being injectedtherein by metered delivery injector 138.

As a result an excess ozone/air mixture is formed in combiner 136.

Reactor 139 in which the mixture can react for a first selected periodwherein excess ozone in the mixture reacts with substantially all nitricoxide in the mixture is operatively coupled to combiner 136.

Photoreactor 140 is also operatively coupled to combiner 136.Illumination source 141 is operatively disposed about photoreactor 140to illuminate the mixture in photoreactor 140 for a second selectedperiod under known temperature and illumination conditions. Illuminationfrom source 141 can be kept constant or can be varied according to apreselected or selected illumination profile. Illuminationcontroller/programmer 142 is operatively coupled to source 141 and anillumination sensor consisting of photodiode 143 and photometer 144 forthis latter purpose.

Temperature sensor 145 is operatively coupled to photoreactor 140 andtemperature controller/programmer 146 to determine the temperature ofthe mixture in photoreactor 140. The temperature of the mixture inphotoreactor 140 can be kept constant during illumination or can beallowed to vary and monitored or can be varied according to apreselected or selected temperature profile by temperaturecontroller/programmer 146 which is operatively coupled to photoreactor140 via lines 147 and 148.

Reactor 149, in which during a third selected period, excess ozone inthe mixture reacts with substantially all nitric oxide is operativelycoupled to photoreactor 140.

Ozone analyser 150 is operatively coupled to reactor 139 to determine afirst ozone concentration of the mixture after the first selected periodat point CI and operatively coupled to reactor 149 to determine a secondozone concentration of the mixture after the third selected period atpoint CII. The mixture is vented from the system via analyser 150 andvent 151. Computer 152 is operatively coupled to temperature sensor 145,photometer 144 and analyser 150 to calculate the rate coefficient fromthe first and second ozone concentrations, the known temperature andillumination conditions and the duration of the second selected period.

The rate coefficient of smog formation in air can be determined in thefollowing manner. A metered amount of air is delivered to combiner 33after passing through filter 131 by injector 132.

Optionally a metered amount of nitric oxide is added to the air incombiner 133 after passing through filter 134 by injector 135 to providea nitric oxide/air mixture in combiner 133. The nitric oxide/air mixtureis delivered to combiner 136. Excess ozone is added to the mixture incombiner 136, after passing through filter 137 by injector 138 toprovide a nitric oxide/excess ozone/air mixture in combiner 136. Themixture is split into two streams, one stream being transferred toreactor 139 and the other to photoreactor 140. The mixture is permittedto react in reactor 139 for a first selected period wherein excess ozonein the mixture reacts with substantially all nitric oxide in themixture. A first ozone concentration of the mixture is then measured byanalyser 150 at point CI. The mixture is illuminated in photoreactor 140for a second selected period under selected and known temperature andillumination conditions. After illumination the mixture is permitted toreact for a third selected period in reactor 149. A second ozoneconcentration of the mixture is measured after the third selected periodat point CII by analyser 150. Preferably the duration of the firstperiod is equal to the total duration of the second and third period.The rate coefficient is then calculated by computer 152 from the firstand second ozone concentrations, the known temperature and illuminationconditions and the duration of the second selected period.

Addition of nitric oxide to air combiner 133 ensures that there issufficient but small concentration of nitric oxide available inphotoreactor 140 to enable reaction (2) not to be limited byinsufficient nitric oxide. Smog production is thus to a goodapproximation equivalent to nitric oxide consumed by reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)ps

The nitrogen dioxide produced quantitatively by reaction (2)subsequently reacts to produce approximate]y equivalent ozone byreaction (3) ##STR8## Thus smog formation in photoreactor 140 can bemeasured according to the increase in ozone concentration produced byreaction in the photoreactor. On this basis the rate coefficient iscalculated by equations (38) and (84).

    R.sub.smog.sup.t =.sup.T,I Q.sub.smog.sup.t /I.sup.t f(T.sup.t)(38)

    where

    f(T.sup.t)=e.sup.-1000γ(1/T.spsp.t.sup.-1/316)       (39)

    and

    γ=4.7

    and

    .sup.T,I Q.sub.smog.sup.t  = {[(.sup.CI χ.sub.O.sbsb.3  - .sup.CII χ.sub.O.sbsb.3 /.sup.II t](v.sub.132  + v.sub.135  + v.sub.138)/v.sub.132 }                                    (84)

where ^(CI) χ_(O).sbsb.3 and ^(CII) χ_(O).sbsb.3 are the ozoneconcentrations at points CI and CII respectively, ^(II) t is theduration of the second selected period and v₁₃₂, v₁₃₅ and v₁₃₈ are thevolumes injected in a specified time by injectors 132, 135 and 138respectively and I is the illumination intensity and T is thetemperature in degrees Kelvin of photoreactor 140.

Referring to FIG. 6 a system 160 for determining rate of smog Formationin air under selected temperature and illumination conditions includesan air filter 151 which filters incoming air and a metered deliveryinjector 162 which delivers a metered dose of the filtered air to afirst combiner 163. A metered dosage of nitric oxide is combined withthe filtered air in combiner 163 after passing through nitric oxidefilter 164 and being injected into combiner 163 by metered deliveryinjector 165.

First combiner 163 delivers the mixture to second combiner 166. Ametered dosage of excess ozone is combined with the mixture in secondcombiner 166 after passing through ozone filter 167 and being injectedinto combiner 166 by metered injector 168. A reactor 169 in which themixture can react for a first selected period wherein excess ozone inthe mixture reacts substantially all nitric oxide in the mixture isoperatively coupled to combiner 165.

Photoreactor 170 is also operatively coupled to combiner 166.Illumination source 171 is operatively disposed about photoreactor 170to illuminate the mixture in photoreactor 170 for a second selectedperiod under selected temperature and illumination conditions.Illumination from source 171 can be kept constant or can be variedaccording to a preselected or selected illumination profile.Illumination controller/programmer 172 is operatively coupled to source171 and an illumination sensor consisting of photodiode 173 andphotometer 174 for this latter purpose.

A temperature sensor 175 is operatively coupled to photoreactor 170 andtemperature controller/programmer 176 to determine the temperature ofthe mixture in photoreactor 170. The temperature of the mixture inphotoreactor 170 can be kept constant during illumination or can beallowed to vary and monitored or can be varied according to apreselected or selected temperature profile by temperaturecontroller/programmer 176 which is operatively coupled to photoreactor170 via lines 177 and 178.

Reactor 179 in which during a third selected period excess ozone of themixture reacts with substantially all nitric oxide is operativelycoupled to photoreactor 170.

Ozone analyser 180 is operatively coupled to reactor 169 to determine afirst ozone concentration of the mixture after the first selected periodat point CI and operatively coupled to reactor 179 to determine a secondozone concentration of the mixture after the third selected period atpoint CII. The mixture is vented from the system via analyser 180 andvent 181.

Computer 182 is operatively coupled to analyser 180 to calculate therate from the first and second ozone concentrations and the duration ofthe second selected period.

The rate of smog formation in air can be determined in the followingmanner. A metered amount of air is delivered to combiner 163 afterpassing through filter 161, and injector 162. Optionally nitric oxide isadded to the air in combiner 163 after passing through filter 164, byinjector 165 to provide a nitric oxide/air mixture in combiner 163.

The mixture is transferred to a second combiner, combiner 166. Excessozone is added to the mixture in combiner 166 after passing throughfilter 167, by injector 168 to provide a nitric oxide/excess ozone/airmixture in combiner 166. The mixture is split into two streams onestream being transferred to reactor 169 and the other to photoreactor170. The mixture is permitted to react in reactor 169 for a firstselected period wherein excess ozone in the mixture reacts withsubstantially all nitric oxide in the mixture. A first ozoneconcentration of the mixture is then measured by analyser 180 at pointCI. The mixture is illuminated in photoreactor 170 for a second selectedperiod under selected temperature and illumination conditions andfurther allowed to react for a third selected period in reactor 179where excess ozone reacts with nitric oxide.

A second ozone concentration of the mixture is measured after the thirdselected period at point CII by analyser 180. Preferably the duration ofthe first period is equal to the total duration of the second and thirdperiods. The rate under selected temperature and illumination conditionsis then calculated by computer 182 from the first and second ozoneconcentrations and the duration of the second selected period.

Addition of nitric oxide to air at combiner 163 ensures that there issufficient but small concentration of nitric oxide available inphotoreactor 170 to enable the rate of reaction (2) not to be limited byinsufficient nitric oxide. Smog production as measured by ozoneformation in photoreactor 170 is thus to a good approximation equivalentto nitric oxide consumed by reaction (2):

    RO.sub.2 +NO→NO.sub.2                               (2)

The nitrogen dioxide produced quantitatively by reaction (2)subsequently reacts to produce approximately equivalent ozone byreaction (3): ##STR9## Thus smog formation in photoreactor 170 can bemeasured according to the increase in ozone concentration produced byreaction in photoreactor 170. On this basis the rate of smog formation(^(T),I Q_(smog) ^(t)) in air under the selected temperature andillumination conditions of photoreactor 170 is calculated according toequation (85):

    .sup.T,I Q.sub.smog.sup.t  = {[(.sup.CI χ.sub.O.sbsb.3  - .sup.CII χ.sub.O.sbsb.3)/.sup.II t][(v.sub.162  + v.sub.165  + v.sub.168)/v.sub.162 ]}                                   (85)

where ^(CI) χ_(O).sbsb.3 and ^(CII) χ_(O).sbsb.3 are the ozoneconcentrations at points CI and CII respectively, ^(II) t is theduration of the second period and v₁₆₂, v₁₆₅ and v₁₆₈ are the volumesinjected in specified time by injectors 162, 165 and 168 respectively.

Referring to FIG. 7 a system 200 for determining extent and maximumpotential smog formation in air includes an air filter 201 which filtersincoming air and a metered delivery injector 202 which delivers ametered dose of the filtered air to combiner 203 and a separate dose ofthe filtered air to NO_(y) converter 209. A metered dosage of excessnitric oxide is combined with the filtered air in combiner 203 vianitric oxide filter 204 and metered delivery injector 205. As a resultan excess nitric oxide/air mixture is formed in combiner 203.

Reactor 206 in which the mixture can react for a selected period whereinthe excess nitric oxide reacts with substantially all ozone the mixtureis operatively coupled to combiner 203. Nitric oxide analyser 207 isoperatively coupled to reactor 206 to determine the nitric oxideconcentration of the mixture at point BI. Analyser 207 is operativelycoupled to reactor 206 via converter 208 which converts all the NO_(y)in the mixture to nitric oxide so that the NO_(y) concentration of themixture can be determined as nitric oxide at point BII by analyser 207.The mixture is vented from the system via analyser 207 and vent 211.

Converter 209 is operatively coupled to analyser 207 via point so thatthe total NO_(y) concentration of the air can be determined as nitricoxide at point AII. The air is vented from the system via analyser 207and vent 211.

Computer 21O is operatively coupled to analyser 207 to calculate themaximum potential and extent of smog formation from the determinedNO_(y) and nitric oxide concentrations of the mixture and the NO_(y)concentration of the air.

The extent and maximum potential smog formation in air can be determinedin the following manner. A metered amount of air is delivered tocombiner 203 after passing through filter 201 by injector 202. Excessnitric oxide is added to the air in combiner 203 after passing throughfilter 204, by injector 205 to provide an excess nitric oxide/airmixture in combiner 203.

The mixture is transferred to reactor 206 where it is permitted to reactfor a selected period wherein excess nitric oxide in the mixture reactswith substantially all ozone in the mixture. The nitric oxideconcentration of the mixture is then measured by analyser 207 at pointBI. The NO_(y) concentration of the mixture is measured as nitric oxideafter passing through converter 208 at point BII.

A metered amount of air is also delivered to nitric oxide analyser 207via converter 209. The NO_(y) concentration of the air is determined atpoint AII as nitric oxide after passing through converter 209.

The extent (E_(smog) ^(t)) and maximum potential smog formation (^(fmax)χ_(smog) ^(t)) is then calculated by computer 210 from the NO_(y)concentration of air and the mixture and the nitric oxide concentrationof the mixture according to equation (33) and equations (86), (87) and(88):

    .sup.fmax χ.sub.smog.sup.t  = β(.sup.AII χ.sub.NO.sup.t  + P.sub.7,2.sup.f χ.sub.smog.sup.t)                     (86)

    and

    .sup.f χ.sub.smog.sup.t  = {[χ.sub.smog.sup.t -(1- .sup.o F.sub.NO).sup.AII χ.sub.NO.sup.t ]/ (1- .sup.o F.sub.NO P.sub.7,2)}(87)

    and

    χ.sub.smog.sup.t  = [(.sup.BII χ.sub.O  - .sup.BI χ.sub.NO) (v.sub.202  + v.sub.205)/v.sub.202 ]                      (88)

where ^(AII) χ_(NO), ^(BI) χ_(NO), ^(BII) χ_(NO) are the nitric oxideconcentrations measured at AII, BI and BII respectively and v₂₀₂ is thevolume of air injected by injector 202 into combiner 203 and v₂₀₅ is thevolume of gas injected by combiner 205 in a specified time and where thevalues of β, P₇,2 and ^(o) F_(NO) are approximated by β=4, P₇,2 =0.125and ^(o) F_(NO) =0.9 and the extent of smog formation in air (E_(smog)^(t)) that is the proportion of smog produced to the maximum potentialamount of smog produced is calculated from equation (35):

    E.sub.smog.sup.t =.sup.f χ.sub.smog.sup.t /.sup.fmax χ.sub.smog.sup.t                                      (35)

FIGS. 8 and 9 depict a preferred photoreactor for use in a system of theinvention and a schematic cross-section of the edge of this photoreactorrespectively.

When designing a photoreactor for use in a system of the invention it isdesirable to:

(a) minimise the extent to which chemical reactions occur on the surfaceof the photoreactor;

(b) provide for the transmission of both UV and visible light throughthe walls of the photoreactor;

(c) ensure that the sample within the photoreactor is well mixed; and

(d) purge the housing containing the photoreactor with purified air soas to minimize the possibility of contamination of the photoreactor bythe ambient or room air and the possible diffusion through the walls andinto the photoreactor of reactive species which may be present in theair surrounding the reactor.

Referring to FIG. 8 reactor 300 has walls 301 consisting of two sheetsof thin FEP teflon film, supported by and sealed at frame 302. Frame 302is held by bracing pieces 303. An excess nitric oxide or ozone/airmixture is directed into photoreactor 300 via inlet tube 304 and leavesphotoreactor 300 via teflon feed-through tube 305 which penetrates walls301 at point 306. The excess nitric oxide or ozone/air mixture passes asa jet stream into photoreactor 300 from inlet end 307 and thus stirs themixture in photoreactor 300. The excess nitric oxide or ozone/airmixture leaves photoreactor 300 via exit end 308. At least a portion ofinlet tube 304 fits inside outlet tube 305. This arrangement isparticularly satisfactory since only one feed-through port is requiredin walls 301. Frame 302 retains two gaskets forming a seal and isdescribed in detail below with reference to FIG. 9.

FIG. 9 shows a sectional view of frame 302 which includes two pieces ofshaped aluminium D-section rod. Two sheets of FEP teflon film which formreactor walls 301 are held with the inside faces of frame 302 by twogaskets 309 to provide a gas tight seal between reactor film walls 301.The gaskets 309 are formed from sheet elastomeric material, Viton (trademark) rubber being suitable. The assembly of frame 302, gaskets 309 andreactor walls 301 are secured together by screw fasteners 310 and 311.

The advantage of using FEP teflon film for walls 301 is that it isunreactive. Contact between FEP teflon Film walls 301 and othermaterials, e.g. metal of frame 302 is minimized in photoreactor 300 thusreducing the extent to which active species can diffuse through walls301 and contact frame 302 or gaskets 309, undergo reactions andrediffuse back into reactor 300. Further, in photoreactor 300, frame 302and bracing pieces 303, are minimized in area so as to minimizeabsorption of radiant energy by frame 302 and pieces 303 thus minimizingheat transferred to the mixture in photoreactor 300. The mixture withinreactor 300 is kept well stirred by the jet-like action of the incomingmixture from inlet end 307. The use of only two sheets of FEP teflonfilm for walls 301 (thickness approximately 0.025 mm) and a singlecontinuous joint minimizes sealing problems that can occur at cornerjoints. The configuration of photoreactor 300 enables all the mixture inthe photoreactor to be simultaneously illuminated thus avoiding darkreactions which could occur if there were shadows cast by frame 302 onthe mixture in photoreactor 300. The configuration of photoreactor 300enables the volume of the photoreactor to be varied after assembly, byadjustment of the length of bracing pieces 303.

FIG. 10 depicts a preferred nitric oxide analyser for use in a system ofthe invention. FIG. 11 depicts a sample selection valve which togetherwith the radial flow chemiluminescent reactor are two preferredcomponents of the nitric oxide analyser of FIG. 10.

When designing a nitric oxide analyser for use in the system of theinvention it is desirable to achieve an analyser that is highlysensitive to nitric oxide and to:

(a) Provide for the rapid switching between samples.

(b) Minimise the time required to purge the analyser between samples.

(c) Provide the ability to measure small differences in the nitric oxideconcentrations of two sample streams.

(d) Provide the ability to complete rapidly the analysis of six separatestreams (i.e. Streams AI, AII, BI, BII CI, CII).

(e) Provide means to rapidly zero and calibrate the response of theanalyser.

Referring to FIG. 10 the nitric oxide analyser sample stream selectionvalve 400 has eight inlet ports. The sample and mixture streams of thesmog monitor at AI, AII, BI, BII, CI and CII are fed to thecorresponding labelled inlet ports 401 of valve 400 as shown in FIG. 10.Nitric oxide-free air is supplied to inlet port DI and a mixture ofknown nitric oxide concentration is supplied to port DII. Valve 400 hasa common outlet port 402 and eight vent ports 403 which are individuallyconnected to their corresponding inlet ports 401. Gas flow from eachinlet port is switched to either the outlet port 402 or thecorresponding vent ports 403 by means of eight gas switching solenoidvalves. The unselected streams freely vent to waste at vents 403 and asingle selected steam is delivered from outlet 402 to flow divider 404.Flow metering orifice 405 is connected to flow divider 404 and dispensesa metered flow rate of the selected stream into chemiluminescent reactorinlet 408. Flow in excess of that required by metering orifice 405supplied to divider 404 and the excess is freely vented to atmosphere atvent 407. A suitable flow at orifice 405 is 750 scc/min. At the inlet408 to radial-flow chemiluminescent reactor cell 406 the selected andmetered stream is mixed with a metered supply of ozonised air which isprovided by ozoniser 409 and delivered at a constant flow rate bymetering orifice 410 to the reactor inlet 408. The mixture from inlet408 flows with radial flow pattern through the disc shapedchemiluminescent reaction cell 406, passing between mirrored back plate420 and optical filter 413. The mixture passes around the edge of thecircular mirror plate 420 and is exhausted via activated carbon ozonescrubber 411 by vacuum pump 412 and vented to waste. Light produced inthe radial flow chemiluminescent reaction cell 406 by reaction of ozonewith nitric oxide passes through optical filter element 413 and isdetected by photomultiplier 414. Signal output from photomultiplier 414is fed to signal processor 415 via line 416. Controller 417 switchesstream selection valve 400 via line 419 and the selection iscommunicated to signal processor 415 via line 418.

An advantage of the disc shaped radial flow chemiluminescent reactioncell is that for a given cell volume the system has the minimum gasmixture residence time and provides rapid purge out of the cell when anew sample stream is selected at valve 400. This arrangement alsoprovides good optical coupling with the photocathode of thephotomultiplier. Utilization of mirror backed glass disc back plate 420in the reaction cell 406 further enhances the intensity of lightcollected at the photocathode of photomultiplier 414. A suitabledimension for the reaction cell 406 is 6 mm by 55 mm diameter andtypically the cell is operated at a pressure of 1/10 atmosphere or lessand which is maintained by vacuum pump 412.

FIG. 11 shows a schematic representation of a preferred sample streamselection valve 400, a component part of the nitric oxide analyser.Valve 400 has a stainless steel body 423 and eight inlet ports 401disposed symmetrically about a centrally located common outlet port 402.Each inlet port 401 is connected with an associated vent port 403 andalso to the outlet port 402 via outlet manifold 426. Flow from inletports 401 is directed either to manifold 426 via valve seats 425 when425 is open or to vent ports 403 when valve seat 425 is closed. Thevalve plunger 428 is activated by solenoid 430 and can take up twopositions:

(1) normally closed;

valve seat 425 is closed and valve seat 429 is open to allow flow frominlet port 401 to vent freely to atmosphere via the corresponding vent403; and

(2) open;

solenoid 430 is energised, plunger 428 is withdrawn against returnspring 431 to close valve seat 429 to open seat 425, directing flow frominlet 401 via drilling 427 to manifold 426 and out of the valve body 423via common outlet port 402.

The volume of manifold 426 is small as also is the volume of the valveseat to manifold drillings 427. The drillings 427 are short to minimizedead volume and to ensure rapid purging of the manifold assembly whenflow streams are switched by the action of the solenoids 430.

In operation each stream flows through its respective inlet port 401into valve body 423. Only one solenoid 430 is energised at any time. Thestream with the energised solenoid passes out of the valve via valveseat 425, drilling 427 manifold 426 and outlet port 402. The stream ofthe unenergised solenoids flow freely through their respective solenoidvalves passing plungers 428 and valve seat 429 to vent at vent 403.Inlet ports 401 are disposed close to their corresponding valve seats425 thus ensuring that when unenergised each solenoid valve iscontinuously well purged with the gas stream.

An advantage of this design of valve 400 is that it enables severalstreams to be independently and rapidly switched into a common manifold.Because the volume of manifold 426 is small and drillings 427 are shortthe dead volume of the system between valve seats 425 and outlet port402 is small. Thus the gas of any selected stream is rapidly displacedfrom manifold 426 by the next selected stream when the solenoidselection is changed. Bleed of the previous sample from drillings 427into the newly selected stream is minimised by making drillings 427short. Thus stream selection valve 400 requires only a very short timeperiod to completely purge out with each newly selected stream.

The outlet port 402 is connected to chemiluminescent reaction cell 406via stream divider 404 by short lengths of tubing of small volume.

The advantage of using a radial flow chemiluminescent reaction cellcoupled with small dead volume stream selection valve 400 is that itenables the nitric oxide analyser of FIG. 10 to be rapidly switched fromsample stream to stream with minimum time required between measurementsfor purge out of the previous sample stream from the analyser beforecommencment of measurement of the newly selected stream.

The advantage of rapidly switching between streams is that when thenitric oxide concentration difference between streams is to bedetermined and the composition of the air sampled by the smog monitor isvariable the error in the concentration difference measurement isminimised when the time difference between the measurement of eachstream is minimised.

The nitric oxide analyser is operated in the following manner. Streamselection is controlled by controller 417 which selects streamsaccording to the following routine, activating the selected solenoids ofvalve 400 via communication line 419. Controller 417 operates two kindsof cycles, X and Y. Cycle X provides analysis of streams AI through toCII. The time taken for analysis of each stream is composed of the timerequired to purge the previous stream from the analysis system (timeperiod m) and a second period when the uncontaminated stream is analysedfor a time period equal to an integral multiple of time period n. CycleX has the sequence:

    AI(m,n), AII(m,n), BI(m,n), BII(m,n), CI(m,n), CII(m,2n), CI(m,n)

where AI(m,n) denotes stream AI selected and for period m+n.

During time period m the nitric oxide analyser is purged by the newlyselected AI stream without data processor 415 recording the output fromthe photomultiplier 414.

Following completion of period M controller 417 activates dataacquisition by data processor 415 of output signal from photomultiplier414 for a period n. On completion of the n time period controller 417stops acquisition of data by 415 and immediately deselects port AI andselects port AII valve 400 and similarly through the rest of the cycle,except that for CII measurement data is acquired for a period ofduration 2n.

Cycle Y contains the same sequence as cycle X but in addition includesselection of either port DI or DII.

Cycle Y has the sequence:

    AI(m,n), AII(m,n), BI(m,n), BII(m,n), CI(m,n), CII(m,2n), CI(m,n), D[I or II](m,n)

A suitable time for completion of either cycle X or Y is 45 seconds anda suitable value for m is 0.714 seconds.

The duration of period n is different from cycles X and Y.

For cycle X, m=5.0 seconds and for cycle Y, m=4.36 seconds.

Typically the smog monitor operates with controller 417 directingcompletion of three X cycles followed by a Y cycle every fourth cycle,with stream DI being activated during the Y cycle, thus providing a zeroNO concentration reference point for the nitric oxide analyser.

From time to time the nitric oxide analyser is calibrated, typicallyonce per day, by substitution of one of the X cycles every fourth cycleby a Y cycle wherein stream DII is selected. Port DII of valve 400 isprovided with a calibration gas mixture of known nitric oxideconcentration during the period of the calibration which is typically 15minutes.

The advantages of this arrangement are:

The nitric oxide analyser can be zeroed and calibrated withoutinterruption to the analysis of streams AI to CII.

Analysis of all the required streams is rapidly completed in the spaceof 45 seconds. Rapid completion of the measurement cycle minimises thelikelihood that the composition of the air being sampled and analysedwill vary significantly during the course of a single cycle, thusminimising the error in the values determined for the nitric oxideconcentration difference between streams.

It is desirable to determine the nitric oxide concentration differencebetween streams CI and CII to higher accuracy than is required for theAI, AII and BI, BII concentration differences. The analyser providesvery accurate measurement of small nitric oxide concentrationdifferences between stream CI and CII by devoting proportionally greatertime to measurement of these streams and by measuring the CI stream bothimmediately before and immediately following the CII measurement.

AN EXAMPLE OF THE INVENTION AND APPLICATION TO PHOTOCHEMICAL SMOGMONITORING

An example of system 100 was fabricated substantially in accordance withthat described with reference to FIG. 4 and as shown in FIG. 12.

Reactor 107 was fabricated from FEP (Trade Mark) Teflon film (registeredTrade Mark) with an internal volume of 17 liters.

Reactors 116 and 118 were of identical construction, which consisted ofa PTFE Teflon pipe or internal diameter 40 mm and length 1000 mm (Volume1.26 liters), with end closures of PTFE teflon and with mixture inletand outlet at opposing ends,

Reactors 106 and 106A were a combination of reactors identical with theconfiguration of reactors 107 and 116 respectively.

Illumination source 108 was a combination of several fluorescent UVlights with light output rich in the UVA region of the spectrum togetherwith white light fluorescent lamps. Illumination intensity was keptconstant when the system was in operation. Source 108 had a total powerconsumption of 440 watts.

Twenty two fluorescent lamps 108 were disposed about photoreactor 107.

The lamps are separated from photoreactor 107 by an airtight FEP Teflonfilm window 500. Photoreactor 107 is located centrally within airtightchamber 501 formed by window 500. Reactor 106 is surrounded by an opaqueairtight housing 502 forming chamber 503 about reactor 106 and housing502 is connected to chamber 501 by two ventilation lines 504 and 505.Line 504 included blower 506 to circulate purified air between chambers501 and 503.

Heat exchanger 509 is mounted in the circulating purified air flow. Thetemperature within chambers 500 and 502 is sensed by temperature sensor507 and the temperature of the purified air controlled to a selectedtemperature by controller 508 and heat exchanger 509. Temperature sensor507 is linked to controller 508 by line 510 and temperature controller508 to heat exchanger 506 by line 511.

The temperature was selected on the basis of being as warm as wascompatible with smog formation under the ambient conditions to bemeasured, so as to cause the rate of reactions in photoreactor 107 to besufficiently fast, the sensitivity of measurement of rate of smogformation being greater the higher the temperature (and light intensity)of photoreactor 107. The maximum temperature desirable is limited by theonset of reactions which do not take place in the atmosphere.

On these grounds the selected temperature was 40° C.

Maintaining the temperature of reactors 106 and 107 warmer than that ofthe air to be measured minimizes the likelyhood of condensation of wateror reaction products onto the walls of reactors 106 or 107.

A supply of purified air was provided by air purifier 512 (AADCO 737series, AADCO, Inc., 2257 Lewis Avenue, Rockville, Md. 20851, U.S.A.)and supplied to housing 503 via line 510 and excess air freely exhaustedfrom chamber 503 and vent 514. By purging chambers 503 and 501 withpurified air, photoreactor 107 is maintained in an environment withminimal ROC and NO_(y) concentrations, thus reducing the likelihood ofcontamination of reactor 106 and photoreactor 107 by air of the roomwithin which system 100 was located, including diffusion of reactivecontaminants through the FEP Teflon film walls.

The materials of fabrication of all components were chosen on the basisthat there would be minimum outgassing therefrom. For example, materialswith plasticizers were not employed.

Teflon insulated wires were used to link the sensors in system 100 andTeflon tubes were used to link the components with the reactors ofsystem 100.

Reactors 106 and 107 were maintained at a common constant temperature of40° C. by temperature controller 508.

Nitric oxide gas was supplied to filter 104 as a mixture of about 800ppm nitric oxide in nitrogen and was injected by metered deliveryinjector 105 at a constant rate of 1.8 ml per minute.

The flowrate of mixture through reactor 118 was maintained at 0.38liters/min and through reactors 106 and 106A, and photoreactor 107 andreactor 116 at 1.47 liters/min.

Analyser 117 was capable of determining nitric oxide concentration oftwo gas streams simultaneously and computer 122 calculated theconcentration and concentration difference of each pair of streams AIand AII, BI and BII or CI and CII. Analyser 117 was configured todetermine nitric oxide concentration at points AI and AII forapproximately 5 minutes, then at BI and BII for five minutes and then atCI and CII for a further five minutes and then continue by repeating thecycle indefinitely.

The residence time of mixture flowing in plug flow through reactor 118was approximately 3.3 minutes and the residence time of mixture in wellstirred photoreactor 107 was 11.6 minutes and residence time reactor 116under conditions of plug flow, 0.86 minutes. The residence time ofmixture in reactors 106 and 106A was equal to the sum of the residencetimes of reactors 107 and 116, namely 12.6 minutes. Thus because of thediffering residence time for streams emerging at AI, AII, BI, BII, CIand CII to pass through system 100 via the various flow paths fromfilter 101 to analyser 117 and the sequential analysis of air andmixture passing points AI, AII, BI, BII, CI and CII, the air and mixturemeasured at points AI, AII, BI, BII, CI and CII within any one analysercycle represented separate sub samples of air which passed as a singlesample through filter 101.

Thus to a fair approximation, analyses made at points AI, AII, BI, BII,CI and CII within the one nitric oxide analyser measurement cyclerepresent separate analyses of the same air. This is advantageous whenthe composition of air entering filter 101 is variable, as is frequentlythe case when ambient air is monitored.

In this example of the operation of system 100 it was located in therural outskirts of a major city, approximately 16 km from the centralbusiness district and some kilometers from any known strong source ofROC or nitrogen oxides emissions. The topography of the region wasgenerally fiat, with no significant mountains or hills. The locality isknown to be subject periodically to episodes of photochemical smog. Theatmosphere at the location was sampled directly into filter 101.

The illumination intensity in photoreactor 107 provided by source 108was determined by calibration of the system in the following manner.

Pure air, free of ROC and nitrogen oxides, was supplied throughout thecalibration procedure to filter 101. The system was operated asdescribed for smog monitoring until steady and equal nitric oxideconcentrations were measured by analyser 117 at points CI and CII.Cycling of analyser 117 was then reprogrammed so that points CI and CIIwere measured frequently for the remaining duration of the calibrationprocedure. A known small amount of ROC (^(o) n_(ROC)(std)) of known smogforming activity (a_(ROC)(std)) was then rapidly introduced into thepurified air entering filter 101. The nitric oxide concentration at CIand CII was analysed by analyser 117 for a period of an hour afterintroduction of the ROC mixture.

The ROC mixture employed as the calibration standard and introduced atfilter 101 consisted of a mixture of gaseous alkane, alkene and alkynehydrocarbons and had an activity coefficient for smog formation value of

a_(ROC)(std) =0.016 moles smog/mole ROC/unit illumination/unit f(T)where illumination is expressed in units of ∫k₃.dt, k₃ being the ratecoefficient for NO₂ photolysis. The mean molecular weight of theROC(std) mixture was:

    MW.sub.ROC(std) =31.8 g

An amount of 1.53×10⁻⁴ g of the ROC calibration standard was introducedinto system 100 at filter 101 giving an initial amount of ROC inphotoreactor 107 of 7.00×10⁻⁵ g (2.20×10⁻⁶ moles) which was then subjectto continuous dilution by the flow of ROC-free mixture throughphotoreactor 107 and to photoreaction by illumination provided by source108. These processes can be described by the mechanism: ##STR10## wherethe rate coefficients for dilution of ROC (k₉₀) and dilution of smog(k₉₂) are equal, i.e.:

    k.sub.90 =k.sub.92                                         (93)

thus the smog concentration in photoreactor 107 after introduction ofthe calibration standard at time t=O, is described by ##EQU7##Integration of (95) equation yields

    χ.sub.ROC.sup.t =χ.sub.ROC.sup.t=o e.sup.-k.sbsp.90.sup.t(96)

Substitution of expression (96) for χ_(ROC) ^(t) in equation (94) andk₉₀ for k₉₂ and integrating gives:

    χ.sub.smog.sup.t =k.sub.91 χ.sub.ROC te.sup.-k.sbsp.90.sup.t(97)

Now the rate coefficient for exponential dilution, (k_(dll)) is givenby:

    k.sub.dil =f/V                                             (98)

where f is the flowrate and V the volume of the vessel. Therefore forphotoreactor 107 under the conditions of the calibration:

    k.sub.90 k.sub.92 =1.47/17=8.52×10.sup.-2 min.sup.-1

Now by design and under the specified operating conditions of system 100the smog concentration produced by photoreaction in photoreactor 107 isequivalent to the difference in nitric oxide concentrations between thecorresponding mixture from reactor 106A when measured at CI and themixture From reactor 116 measured at point CII:

    χ.sub.smog.sup.t =.sup.CI χ.sub.NO.sup.t -.sup.CII χ.sub.NO.sup.t                                        (99)

Substitution of the expression (99) into equation (97) yields, for thecalibration:

    .sup.CI χNO.sup.t -.sup.CII χ.sub.NO.sup.t k.sub.91 χ.sub.ROC.sup.t=o te.sup.-k.sbsp.90.sup.t             (100)

Thus for calibration the value of ^(CI) χ_(NO) ^(t) -^(CII) χ_(NO) ^(t)indicated by computer 122 is proportional to the value of te^(-k) 90^(t)and the plot of (^(CI) χ_(NO).sbsb.t=o^(t) -^(CII) χ_(NO) ^(t)) versuste^(-k) 90^(t) has the gradient of k₉₁ χ_(ROC) ^(t=o), where in thepresent case k₉₀ has the value 8.52×10⁻² min⁻¹ and t is the timeduration after introduction of the ROC calibration mixture intophotoreactor 107. For the case of this example the values obtained forthese quantities at various elapsed times are listed in Table 1 and areplotted in FIG. 13, which also shows the line of best fit, which has agradient of 0.0139 and intercept of 0.0029.

To a fair approximation and to the precision of analyser 117 the data ofTable 1 fall on a straight line. This indicates that:

(1) Rate of smog formation is independent of the duration of thereactions involving ROC.

(2) Rate of smog formation is proportional to the amount of ROC presentin air.

(3) Processes occurring at the walls of the reactors 106, 106A and 116and photoreactor 107 do not contribute significantly to the chemicaldynamics of the system.

The line of best fit passes close to but not through the origin, thisintercept is attributable to small errors in the estimation of theinitial time and the initial inhomogeneity of ROC distribution inphotoreactor 107 immediately on introduction of the ROC calibrationmixture.

Thus by equation (100) and the gradient of the graph of FIG. 13

    k.sub.91 χ.sub.ROC.sup.t=o =0.0139×10.sup.-6 mole fraction min.sup.-1                                                (101)

An alternative to determination of k₉₀ by measurement of photoreactor107 volume and flowrates is available by application of data from Table1.

When

    χ.sub.smog.sup.t(1) =χ.sub.smog.sup.t(2)

    then

    k.sub.90 =(1n t(2)-1n t(1))/(t(2)-t(1))                    (102)

where t(1) and t(2) are any two times (t(2)>t(1)) when the respectivesmog concentrations of photoreactor 107 are equal.

An advantage of calibration by introduction of ROC into system 100 asdescribed is that the system performance over a wide range of ROCconcentrations can be evaluated. In the case of this example thequantity of ROC initially present in photoreactor 107 was, in terms ofconcentration, 7.70 ppmC (where ppmC denotes mole carbon X 10⁶ /molemixture). After 59 minutes, dilution reduces this concentration inphotoreactor 107 to 0.050 ppmC.

Now by definition the rate of smog formation in photoreactor 107 (^(T),IQ_(smog) ^(t)) is given by:

    .sup.T,I.sub.Q.sub.smog.sup.t =k.sub.91 χ.sub.ROC.sup.t(103)

where T and I are the temperature and illumination intensityrespectively of photoreactor 107. From (101) and (103) therefore, ^(T),IQ_(smog) ^(t=0) =0.0139 ppm.min⁻¹ for the conditions of the calibration.

Now also for the conditions of photoreactor 107 and by equations (38)(39) and (41) ^(T),I Q_(smog) ^(t) is also given by: ##EQU8##Substitution of the calibration value for ^(T),I Q_(smog) ^(t=0) intoequation (104) and from the known values of the other terms and wherei=ROC calibration mixture the illumination intensity I^(t) isdetermined. ##EQU9## That is the value of k₃ for photoreactor 107 andillumination source 108 assembly is determined to be 0.227 min⁻¹.

The calibration procedure as described is also suitable for determiningthe value of the activity coefficient for smog formation (a_(ROC)) ofparticular ROC or ROC mixtures. This is accomplished by firstdetermining the value of I^(t) for the photoreactor 107 then introducinga known quantity of the ROC/ROC mixture to be evaluated as for the ROCcalibration mixture during calibration. The value of a_(ROC) is thendetermined from the measurements by evaluation of equation (104) usingthe known value of I^(t).

System 100 was installed at the described location and operated tomonitor throughout a day smog in the atmosphere, analysing aircontinuously sampled over the period 0958 to 1654 hours. The temperatureof the atmosphere and the sunlight intensity was measured by sensors 123and 124 respectively for the same day for the selected period of 0622 to1826 hr, these times corresponding approximately with dawn and dusk. Thevalues for the temperature and sunlight intensities at selected timesthroughout the day are given in Table 2. The nitric oxide concentrationsmeasured by analyser 117 at points AI, AII, BI, BII, CI and CII and thecorresponding time of sampling the air (t) are listed in Table 3. Therate of smog formation (^(T),I Q_(smog) ^(t)) for air withinphotoreactor 107 was calculated according to equations (55) and (56) andwhere ^(I) χ_(NO) and ^(III) χ_(NO) of equation (55) correspond to ^(CI)χ_(NO) ^(t) and ^(CII) χ_(NO) ^(t) of Table 3 and T and I are thetemperature and illumination conditions within photoreactor 107 Valuesof ^(T),I Q_(smog) ^(t) determined for each measurement time are listedin row 8 of Table 3. Instrument transients can give rise to spuriousvalues for ^(T),I Q_(smog) ^(t) as is illustrated by the negative valueobtained in Table 3 for time 1044.

The rate coefficient for smog formation R_(smog) ^(t) is calculated fromthe known temperature and illumination conditions of photoreactor 107and the value of ^(T),I Q_(smog) ^(t) by equations (38) and (39). Theresults are expressed as R_(smog) ^(t) ×10⁴ and for each examplemeasurement are listed in row 9 of Table 3 where the units of R_(smog)^(t) are ppm smog/unit of incident light/unit f(T) where the incidentlight intensity is expressed as the rate coefficient for NO₂ photolysis(k₃).

The concentration of smog in air χ_(smog) ^(t) is calculated by equation(57). Values of ^(BI)χ_(NO) and ^(BI) χ_(NO) are listed in Table 3, rows4 and 5, and, for system 100 as employed, v₁₀₂ =1.47+1.47+0.38 =3.38liter min⁻¹ and v₁₀₅ =1.8×10⁻³ liter min⁻¹. The values of χ_(smog) ^(t)determined for each measurement time are listed in row 10 of Table 3.

The NO_(y) concentration of air is measured as nitric oxide at pointAII. For this example the values obtained (^(AII) χ_(NO) ^(t)) arelisted in Table 3, row 3, and are also listed as the NO_(y)concentrations at the time of air sampling (χ_(NO) ^(t)) in row 11 ofTable 3.

The nitric oxide concentration of air is measured at Point AI and thevalues obtained (^(AI) χ_(NO) ^(t)) are listed In Table 3 row 2, and arealso listed in row 12, Table 3, as the nitric oxide concentrations atthe time of air sampling (χ_(NO) ^(t)).

The ozone concentration of air is calculated from the values of χ_(smog)^(t), χ_(NO).sbsb.y^(t) and χ_(NO) ^(t) according to equation (44). Thevalues thus determined (χ_(O).sbsb.3^(t)) are listed in row 13, Table 3for each sampling time.

The concentration at time t of NO_(y) that would exist in the absence ofNO_(y) removal processes from air (^(o) χ_(NO).sbsb.y^(t)), and whichrepresents the cumulative emissions of NO_(y) into air is calculatedfrom the values determined for χ_(NO).sbsb.y^(t), χ_(NO) ^(t) andχ_(O).sbsb.3^(t) as follows.

The value of G is determined by equation (58) and the value of ^(o)χ_(NO).sbsb.y^(t) determined by equation (59) when G^(t) <1 other wiseby equation (60).

The value of G^(t) and corresponding value of ^(o) χ_(NO).sbsb.y^(t) forair at each time of sampling are listed in Table 3, rows 14 and 15respectively.

The maximum potential amount of smog formation in air (^(max) χ_(smog)^(t)) is determined by application of equation (31).

The value thus determined for air at each time of sampling is given inTable 3, row 16.

The extent of prior smog formation in air (^(f) χ_(smog) ^(t)) iscalculated from the measurements according to equation (61) andaccording to the value of G^(t) and where P₇,2 =0.125 and ^(o) F_(NO)=0.9. The values thus determined for ^(f) χ_(smog) ^(t) are given inTable 3, row 17.

The extent of smog formation in air at time t (E_(smog) ^(t)) iscalculated from ^(f) χ_(smog) ^(t) and ^(max) χ_(smog) ^(t) according toequation (35).

The values of E_(smog) ^(t) determined for air at each time of samplingare given in Table 3, row 18.

The concentration of reactive organic compounds χ_(ROC) ^(t) in air sdetermined from the measured reactivity coefficient for smog formationin air (R_(smog) ^(t)) and a known value for the activity coefficientfor smog formation of the ROC mixture as previously emitted into the airand sampled at time t (a_(ROC) ^(t)). Now the value of a_(ROC) ^(t) canbe separately determined by introducing a known amount of the ROCmixture into the system as described for calibration or, alternatively,a value can be assumed.

For the range of compositions of ROC mixtures commonly emitted intourban air the value of a_(ROC) ^(t) is approximately constant over therange of ROC compositions, Hence it is satisfactory to use a generalvalue of a_(ROC) ^(t). The general value is not determined for theparticular ROC mixture present in air at the time of sampling.

For the air being monitored in the present application a value ofa_(ROC) ^(t) of 0.0067 moles smog/moles of ROC carbon/unitillumination/unit f(T) was chosen as applicable.

The concentration of reactive organic compounds in air at time t(χ_(ROC) ^(t)) is given by equation (105)

    χ.sub.ROC.sup.t =R.sub.smog.sup.t /a.sub.ROC.sup.t     (105)

The concentration of ROC in air thus determined for each time of airsampling according to equation (105) are given in row 19 of Table 3 inunits of carbon atoms of ROC/million molecules of air, (ppmC).

To a good approximation the activity coefficient for smog formation inair (a_(ROC) ^(t)) is independent of the amount of illumination to whichthe ROC/air mixture has been exposed. Thus to a good approximation theconcentration of ROC carbon measured by the system according to equation(105) is equivalent to the total amount of ROC carbon previouslyintroduced into the air thus,

    .sup.o χ.sub.ROC.sup.t =χ.sub.ROC.sup.t            (106)

where ^(o) χ_(ROC) ^(t) denotes the total concentration of ROC carbonpreviously introduced into the air.

Table 3 lists in row 20 the value of ^(o) χ_(ROC) ^(t) thus determinedby equation (106) for each time of air sampling.

The reactive organic compounds to nitrogen oxides emission ratio (^(o)χ_(ROC) ^(t) /^(o) χ_(NO).sbsb.x^(t)) of smog precursor emissions is acharacteristic of air commonly used in air quality evaluations and inthe assessment of the smog forming characteristics of air. The value of^(o) χ_(ROC) ^(t) /^(o) χ_(NO).sbsb.x^(t) is determined by operation ofsystem 100. For fresh emissions and as indicated by equation (10)

    χ.sub.NO.sbsb.x.sup.t =χ.sub.NO.sbsb.y.sup.t       (107)

and also given relation (106) then:

    .sup.o χ.sub.ROC.sup.t /.sup.o χ.sub.NO.sbsb.x.sup.t ≦χ.sub.ROC.sup.t /.sup.o χ.sub.NO.sbsb.y.sup.t(108)

The values of ^(o) χ_(ROC) ^(t) /^(o) χ_(NO).sbsb.x^(t) determinedaccording to equation (108) for each time of air sampling of the exampleare given in Table 3, row 21.

System 100 can be used to determine the nitric oxide and ozoneconcentrations in air by an alternative procedure to that yielding theresults of Table 3, rows 12 and 13. The temperature and illuminationintensity of air is measured by sensors 123 and 124 respectively and thevalue of k₃ ^(t), the rate coefficient for NO₂ photolysis in the airdetermined from the readings. The values of k₃ ^(t) determined for thisexample are listed in Table 2. The nitric oxide and ozone concentrations(χ_(NO) ^(t), χ_(O).sbsb.3^(t)) of air determined according to equations(68), (69) or (73) and (74) depending on the domain of ^(f) χ_(smog)^(t) as given f t by expression (70). Now (70) can be evaluated because,following equation (11):

    .sup.o χ.sub.NO.sup.t =.sup.o F.sub.NO.sup.o χ.sub.NO.sbsb.y.sup.t( 109)

and substituting equation (109) into (78) the specified domain of ^(f)χ_(smog) ^(t) is:

    (.sup.o F.sub.NO -H).sup.o χ.sub.NO.sbsb.y.sup.t <.sup.f χ.sub.smog.sup.t <(.sup.o F.sub.NO +L).sup.o χ.sub.NO.sbsb.y.sup.t(110)

The values defining the range of χ_(smog) ^(t) and the applicability ofequations (68) and (69) are calculated on the basis of the determinedvalues of χ_(NO).sbsb.y^(t) and expression (127) and are listed in Table3, rows 22 and 23 wherein H and L have been assigned the value 1/2. Thetruth or falsity of expression (110) is determined by inspection fromthe data of Table 3, rows 22 and 23 and the results are tabulated inTable 3, row 24 When test (110) has value false χ_(NO) ^(t) andχ_(O).sbsb.3^(t) are calculated according to equations (68) and (69)otherwise equations (73) and (74) are employed. The concentrations sodetermined for each time of sampling air are given in Table 3, rows 25and 26.

The value of k₄ employed in this calculation was taken from theliterature, k₄ =2.66×103³ e^(-1370/T).spsp.t ppm⁻¹ min⁻¹.

The time period required for production of selected amount of smog(^(select) χ_(smog) ^(t)) in air of composition as determined at time tcan be determined by application of system 100 and calculation of timeperiod according to equations (82) and (83). Two applications of thismethod are of special interest, namely determination of the time periodof prior smog formation in air and time period required for smogformation in air to reach maximum extent under selected conditions oftemperature and illumination.

The time period required for maximum smog formation for air ofcomposition as determined for each time of sampling and for temperatureand illumination conditions for the day as measured and tabulated inTable 2 is determined as follows. The amount of extra smog required tobe produced to reach (^(fmax) χ_(smog) ^(t)) is determined from themeasurements according to equation (79).

The time period (t₂ -t₁) where t₁ is the time of sampling and t₂ is thetime of onset (^(fmax) χ_(smog) ^(t)) is determined for the conditionsaccording to equation (80).

The integral can be evaluated for the data according to the trapezoidalrule and where R^(t) is the value of R_(smog) ^(t) determined for air attime of sampling, t₁.

The value of the integral ##EQU10## wheref(T^(t))=e⁻⁴⁷⁰⁰(1/T.spsp.t^(-1/316)) and where t_(dawn) =0622 hr wasevaluated for each time of air sampling and the values obtained aretabulated in Table 2.

Now from equations (79) and (80) (^(fmax) χ_(smog) ^(t)) is attained attime t_(max) for air sampled at time t when ##EQU11## Thus the time atwhich the maximum smog formation would be reached under the selectedconditions of temperature and sunlight intensity observed during the dayat the sampling site and in the absence of further NO_(y) emissions intothe air after the time of air sampling is determined for each samplingtime by evaluation of the left hand side of equation (112) and bydetermining the time corresponding to this value by interpolation of thevalues of ##EQU12##

The values obtained for the left hand side of expression (112) are givenin Table 3, row 27 and the corresponding time of day when maximum smogformation was attained determined by interpolation of data listed inTable 2 for each time of sampling are given in Table 3, row 28 and wherethe value >18 indicates that the potential maximum formation of smog isnot reached before sunset (i.e. t=18) on that day.

The time period (t_(t) -t_(o)) during which smog formation in air hasoccurred may be determined according to equation (81), given that whenthe conditions ^(f) χ_(smog) ^(t) =β^(o) χ_(NO).sbsb.x^(t) is true theperiod determined is a minimum period. Knowledge of the time period andthe time of measurement (t_(t)) enables the apparent time of emission ofROC (i.e. an average time of the ROC emissions weighted with respect tothe ROC emission strengths and sunlight intensities) into the air(t_(o)) to be determined by equation (113), the time corresponding tothe beginning of the smog forming period.

    t.sub.o =t.sub.t -(t.sub.t-t.sub.o)                        (113)

It is convenient to calculate the value of ##EQU13## throughout the day,as given in Table 2. From equations (81) and (113) equation (114) isobtained. ##EQU14##

The times (t_(o)) corresponding to the values determined by equation(114) for ##EQU15## may be obtained by interpolation from Table 2. Thevalues thus determined by application of equation (114) for ##EQU16##and the corresponding values for t_(O), the apparent time of ROCemissions, for air at each time of sampling are given in Table 3 rows 29and 30 and where the value t_(o) of <06 indicates that the ROC enteredthe air previous to the day of measurement. For air that was sampledduring the period 11.29 to 12.30 hrs and at 14.04 hrs the data isconsistent with significant quantities of ROC having been emitted intothe air at about dawn otherwise the results indicate that the smogforming activity of the air sampled during the day is attributable toROC emitted to the air on days previous to the day of measurement.

The general case for determination of time period for production ofselected amount of smog in air is here illustrated by way of example forone air analysis. For air of the same characteristics as the sample thesmog, ozone and nitric oxide concentrations to be expected throughoutthe selected time period, namely from dawn to dusk on the day ofsampling are determined. The air sample for this example is arbitrarilychosen as sampled at 1145 hrs. The procedure described is applicable tosampled at other times. Smog concentrations to be expected at selectedtimes are determined from the data obtained by operation of system 100using equation (81).

For this example the nitrogen oxides determined as present in the air attime of sampling are assumed to have been present throughout theprevious daylight hours. The ROC is taken to be emitted into the air ata single time corresponding to the determined mean time of ROC emission(t_(o)), i.e. 08.30 hr on the day of sampling.

The value of ##EQU17## where t=O is the time of ROC emission aspreviously determined for the 1145 sample (i.e. t=0 corresponding to0830 hrs), is calculated from the data listed in Table 2 for selectedtimes. The values obtained are given in Table 4. The value of ^(o)χ_(NO).sbsb.y^(t) for all values of t is as determined for the sampleair at 1145, i.e. ^(o) χ_(NO).sbsb.y^(t) =0.17 ppm, see Table 3. Thevalue for R_(smog) ^(t) smog prior to the determined time of ROCemission is: R_(smog) ^(t) (t<([t=o])=0.0 while for all times t≧[t=o],R_(smog) ^(t) =8.5×10⁻³ as determined for the 1145 sample and as listedin Table 3. The air temperature at selected times is given in Table 2.The predicted concentrations of smog formed (^(f) χ_(smog) ^(t))calculated using the sunlight data of Table 4 by equation (81) for eachselected time and the results are listed in Table 4. The initial valuefor the nitric oxide concentration is determined from the value for ^(o)χ_(NO).sbsb.y^(t) by application of equation (109) and hence (^(o)F_(NO) having the value 0.9) ^(o) χ_(NO) ^(t=o) has the value of 0.13ppm.

The domain of ^(f) χ_(smog) ^(t) is tested by inequality (110)(0.044<^(f) χ_(smog) ^(t) <0.218).

The value, true (T) or false (F), thus determined for each time aregiven in Table 4.

When condition (110) has value false the nitric oxide concentrations tobe expected at those selected times (χ_(NO) ^(t)) are calculatedaccording to equation (68) when the value is true χ_(NO) ^(t) isobtained by application of equation (73). Similarly ozone concentrationsare determined by equation (69) when the value is false and by (74) whenthe value is true.

The predicted concentrations of nitric oxide and ozone thus determinedfor selected times and for conditions of no dispersion or dilution ofthe air are given in Table 4. The values for light intensity and airtemperature used are given in Table 2.

INDUSTRIAL APPLICABILITY

The methods and systems of the invention have the following industrialapplicabilities:

(a) Total smog concentration of air can be determined by measurement ofa single species, NO, instead of needing to determine NO_(x), NO, O₃,ROC's etc.

(b) Smog forming activity of the air can be directly measured instead ofhaving to estimate it by determination of ROC's, their composition andconcentrations and as well separately modelling the detailed chemistryof the smog-forming process which requires carrying out of complex andapproximate chemical kinetic calculations.

(c) Prospects for smog formation can be assessed in real time.

(d) Ozone and nitrogen oxides concentrations can be determined via theone detector (an NO detector).

(e) The duration of prior smog formation can be determined in astraightforward manner. Prior art gives no satisfactory means ofdetermining duration of prior smog formation.

(f) Prospective course of smog formation can be quantitatively predictedfrom measurement of a single air sample. Prior art offers no alternativemeans for making such predictions from a single instrumental analysis.

(g) A sensitive means for determining the amount of prior ROC andnitrogen oxides emissions into the air, independently of the reaction orlength of the period of residence in the air is made available.Determination of ROC by alternative means gives results which are biasedlow due to transformation by reaction of the ROC emissions into chemicalforms which are not easily detected by existing ROC analysis methods.

(h) A measure of smog formation is made available which variesproportion to the total amount of smog formation (unlike prior types ofmeasurements which determine the concentration of a single species, e.g.NO or O₃, the concentrations of which vary nonlinearly with total smogformation).

(i) Smog formation can be characterised by only three measuredparameters, namely NO_(y) concentration, smog concentration and ratecoefficient for smog formation, instead of having to specify thebehaviour of numerous chemical species.

(j) The location of the sources of ROC emissions can be estimated fromthe duration of smog formation in air and knowledge of the trajectoryand speed of the air during smog formation.

(k) The most effective option for controlling formation of excessiveozone concentrations in air can be determined from the value of extentof smog formation in air. When the extent approaches the value 1 thenminimization of nitrogen oxides is the indicated strategy. When extentis less than 1 then control of ROC emissions is the indicated strategy.

(l) The concentrations of nitrogen oxides converted to nitric acid orlost from the gas phase can be determined. This is of particularpractical importance as it is a measure of the quantity of nitrogenavailable for acidic or nitrate deposition from the air.

                  TABLE 1                                                         ______________________________________                                        Data measured for calibration of Reactor 107                                            .sup.CI X.sub.NO .sup.t - .sup.CII X.sub.NO .sup.t                                          te.sup.-k 90.sup.t                                    (min)     (ppm)         (k.sub.90 = 8.52 × 10.sup.-2)                   ______________________________________                                         0        0.0000        0.00                                                   1        0.0154        0.92                                                   2        0.0280        1.69                                                   3        0.0350        2.32                                                   4        0.0420        2.84                                                   5        0.0490        3.27                                                   6        0.0490        3.60                                                   7        0.0546        3.86                                                  17        0.0595        3.99                                                  18        0.0581        3.88                                                  19        0.0567        3.76                                                  20        0.0525        3.64                                                  31        0.0336        2.21                                                  32        0.0350        2.09                                                  33        0.0315        1.98                                                  44        0.0175        1.04                                                  45        0.0168        0.97                                                  46        0.0182        0.91                                                  57        0.0084        0.44                                                  58        0.0077        0.41                                                  59        0.0084        0.39                                                  ______________________________________                                         Line of best fit: (.sup.CI X.sub.NO .sup.t - .sup.CII X.sub.NO .sup.t) =      0.0139 te.sup.-0.0852t + 0.0029                                          

                  TABLE 2                                                         ______________________________________                                        Measured temperature and sunlight intensities                                 of the atmosphere for                                                         selected period including the period of operation                             of System 100 in FIG. 12                                                       (hr, min)of Day (t)Time                                                               (T.sup.t, °K.)Temperature                                                         (k.sub.3.sup.t, min.sup.-1)IntensitySunlight                                            ##STR11##                                       ______________________________________                                        06.22   285        0.000     0.0                                              06.37   284        0.009     0.0                                              06.52   283        0.008     0.0                                              07.07   283        0.062     0.1                                              07.22   284        0.071     0.3                                              07.37   286        0.093     0.6                                              07.52   287        0.123     0.9                                              08.07   288        0.137     1.4                                              08.22   290        0.166     1.9                                              08.30   --         --        2.3                                              08.37   292        0.198     2.7                                              09.52   293        0.182     3.6                                              09.07   293        0.218     4.5                                              09.22   295        0.234     5.6                                              09.37   297        0.260     7.0                                              09.42   296        0.304     7.5                                              09.58   298        0.305     9.4                                              10.13   295        0.352     11.2                                             10.29   296        0.364     13.3                                             10.44   297        0.379     15.3                                             10.59   297        0.272     17.2                                             11.13   298        0.397     19.0                                             11.29   297        0.402     21.6                                             11.45   297        0.406     24.1                                             12.00   298        0.415     26.5                                             12.31   298        0.431     31.8                                             13.02   298        0.392     37.0                                             13.33   299        0.426     42.3                                             14.04   299        0.349     47.4                                             14.51   299        0.338     54.5                                             15.22   301        0.359     59.5                                             15.53   301        0.325     64.6                                             16.24   299        0.292     69.0                                             16.54   298        0.280     72.7                                             17.25   298        0.225     75.8                                             17.55   297        0.151     78.1                                             18.26   296        0.000     79.0                                             ______________________________________                                    

    TABLE 3      Example of Smog Monitoring Data obtained by operation of System 100     depicted in FIG. 12 Row t        1 Time of air 0958 1013 1029 1044 1059 1113 1129 1145 1200 1231 1302     1333 1404 1451 1522 1553 1624 1654  Sampling (hr, min)  2 .sup.AI     χ.sub.NO.sup.t (ppm) 0.001 0.006 0.005 0.004 0.004 0.011 0.021 0.025     0.023 0.015 0.005 0.000 -0.001 -0.001 -0.003 -0.003 -0.002 -0.002  3     .sup.AII χ.sub.NO.sup.t (ppm) 09.016 0.028 0.027 0.031 0.038 0.086     0.126 0.151 0.156 0.127 0.085 0.044 0.024 0.017 0.006 0.007 0.005 0.006     4 .sup.BI χ.sub.NO.sup.t (ppm) 0.260 0.291 0.284 0.266 0.249 0.241     0.258 0.262 0.254 0.226 0.187 0.136 0.173 0.190 0.185 0.191 0.208 0.206     5 .sup.BII χ.sub.NO.sup.t (ppm) 0.331 0.343 0.342 0.346 0.353 0.401     0.441 0.466 0.471 0.442 0.400 0.359 0.339 0.332 0.308 0.315 0.317 0.316     6 .sup.CI χ.sub.NO.sup.t (ppm) 0.293 0.292 0.285 0.269 0.254 0.243     0.250 0.259 0.245 0.220 0.180 0.132 0.169 0.191 0.203 0.190 0.205 0.206     7 .sup.CII χ.sub.NO.sup.t (ppm) 0.292 0.290 0.285 0.272 0.251 0.241     0.237 0.241 0.234 0.210 0.175 0.128 0.161 0.186 0.202 0.188 0.202 0.205     8 .sup.T,I Q.sub.smog.sup.t × 10.sup.4 0.9 1.7 0.0 (-2.6) 2.6 1.7     11.2 15.6 9.5 8.7 4.3 3.5 6.9 4.3 0.9 1.7 2.6 0.9  (ppm/min)      9 R.sub.smog.sup.t × 10.sup.4 4.4 8.8 0.0 (-13) 13 8.8 57 79 48     44 22 18 35 22 4.4 8.8 13 4.4 10 χ.sub.smog.sup.t (ppm) 0.07 0.05     0.06 0.08 0.10 0.16 0.18 0.20 0.22 0.22 0.21 0.22 0.18 0.14 0.14 0.12     0.11 0.12 11 χ.sub.NOy.sup.t (ppm) 0.02 0.03 0.03 0.03 0.04 0.09     0.13 0.15 0.16 0.13 0.08 0.04 0.02 0.02 0.01 0.01 0.00 0.01 12 χ.sub.     NO.sup.t (ppm) 0.00 0.01 0.00 0.00 0.00 0.01 0.02 0.02 0.02 0.02 0.00     0.00 0.00 0.00 0.00 0.00 0.00 0.00 13 χ.sub.0.sbsb.3.sup.t (ppm)     0.06 0.03 0.04 0.05 0.07 0.08 0.08 0.08 0.08 0.10 0.13 0.18 0.15 0.12     0.14 0.12 0.10 0.11 14 G.sup.t 0.62 0.26 0.33 0.40 0.41 0.23 0.17 0.14     0.14 0.20 0.39 0.82 1.11 0.98 1.46 1.37 2.29 1.32 15 .sup.o      χ.sub.NOy.sup.t (ppm) 0.03 0.03 0.03 0.04 0.05 0.11 0.15 0.18 0.18     0.16 0.11 0.07 0.05 0.04 0.04 0.04 0.03 0.04 16 .sup.fmax      χ.sub.smog.sup.t 0.10 0.14 0.14 0.17 0.21 0.43 0.60 0.71 0.74 0.62     0.46 0.30 0.19 0.16 0.17 0.15 0.13 0.14  (ppm) 17 .sup.f      χ.sub.smog.sup.t (ppm) 0.08 0.06 0.06 0.09 0.11 0.17 0.19 0.21 0.23     0.23 0.23 0.25 0.19 0.16 0.18 0.16 0.13 0.14 18 E.sub.smog.sup.t 0.75     0.40 0.44 0.52 0.54 0.44 0.32 0.30 0.31 0.37 0.51 0.82 1.00 1.00 1.00     1.00 1.00 1.00 19 χ.sub.ROC.sup.t (ppmC) 0.07 0.13 0.00 -0.20 0.20     0.13 0.85 1.18 0.72 0.66 0.33 0.26 0.52 0.33 0.07 0.13 0.20 0.07 20     .sup.o χ.sub.ROC.sup.t (ppmC) 0.07 0.13 0.00 -0.20 0.20 0.13 0.85     1.18 0.72 0.65 0.33 0.26 0.52 0.33 0.07 0.13 0.20 0.07 21 .sup.o     χ.sub.ROC.sup.t /.sup.o χ.sub.NOx.sup.t 2.5 3.7 0.0 -- 3.8 1.2     5.6 6.6 3.9 4.2 2.9 3.5 10.9 8.4 1.5 3.5 6.0 1.8  (ppmC/ppm) 22 (.sup.o     χ.sub.NO.sup.t - 0.010 0.014 0.014 0.017 0.005 0.010 0.060 0.071     0.074 0.062 0.046 0.030 0.019 0.016 0.017 0.148 0.013 0.014  1/2.sup.o     χ.sub.NOy.sup.t) 23 (.sup.o χ.sub.NO.sup.t + 0.036 0.049 0.049     0.059 0.073 0.149 0.211 0.249 0.259 0.218 0.159 0.105 0.067 0.055 0.060     0.052 0.046 0.050  1/2.sup.o χ.sub.NOy.sup.t) 24 Test (110) (T/F) F     F F F F F T T T F F F F F F F F F 25 χ.sub.NO.sup.t via(68)(73) 0.00     0.00 0.00 0.000.00 0.00 0.02 0.02 0.02 0.00 0.00 0.00 0.00 0.00 0.00     0.00 0.00 0.00  ppm 26 χ.sub.O3.sup.t via(69(74) 0.05 0.02 0.03 0.05     0.07 0.07 0.08 0.08 0.08 0.09 0.13 0.18 0.15 0.12 0.14 0.12 0.10 0.11     (ppm)      27     ##STR12##      69 107 -- --  89 311 94 87 133 122 139 73 46 44 44 57 66 59  28     .sup.max t.sub.smog.sup.t (hr) 16 >18 -- -- >18 >18 >18 >18 >18 >18 >18     17 14 14 14 15 16 15      29     ##STR13##      -168 -52 -- -- -69 -176 -12 3 -20 -20 -68 -98 -8 ≦-26 ≦-34     7 ≦-112 ≦-36 ≦-268  30 t.sub.o (hr) <06 <06 -- --     <06 <06 <06 09 <06 <06 <06 <06 08 <06 <06 <06 <06 <06

                                      TABLE 4                                     __________________________________________________________________________    Concentration-Time Profiles predicted for air with                            characteristics as air                                                        sampled at 11.45 hrs and conditions of                                        temperature and illumination as                                               determined at the sampling site on that day.                                   (hr, min)Time of Day                                                                 ##STR14##                                                                               .sup.f χ.sub.smog.sup.t (ppm)                                                    T/FTest(110)                                                                       (ppm)χ.sub.NO.sup.t Predicted                                                  (ppm)χ.sub.O3.sup.t Predicted          __________________________________________________________________________    0622 (dawn)                                                                          0.0       0.0    F    0.17 0.00                                        0637   0.0       0.0    F    0.17 0.00                                        0652   0.0       0.0    F    0.17 0.00                                        0707   0.0       0.0    F    0.17 0.00                                        0722   0.0       0.0    F    0.17 0.00                                        0737   0.0       0.0    F    0.17 0.00                                        0752   0.0       0.0    F    0.17 0.00                                        0807   0.0       0.0    F    0.17 0.00                                        0822   0.0       0.0    F    0.17 0.00                                        ROC determined as being introduced into air at 0830                           0830   0.0       0.0    F    0.17 0.00                                        0837   0.38      0.00   F    0.17 0.00                                        0852   1.24      0.01   F    0.16 0.00                                        0907   2.17      0.02   F    0.16 0.00                                        0922   3.29      0.03   F    0.15 0.00                                        0937   4.65      0.04   F    0.14 0.00                                        0942   5.17      0.04   F    0.14 0.00                                        0958   7.03      0.06   F    0.12 0.00                                        1013   8.87      0.07   F    0.11 0.00                                        1029   10.93     0.09   T    0.10 0.00                                        1044   13.00     0.10   T    0.09 0.01                                        1059   14.84     0.12   T    0.08 0.01                                        1113   16.68     0.13   T    0.07 0.02                                        1129   19.23     0.15   T    0.06 0.03                                        1145   21.76     0.17   T    0.05 0.04                                        1200   24.19     0.19   T    0.04 0.05                                        1231   29.49     0.23   T    0.03 0.08                                        1302   34.71     0.28   F    0.00 0.10                                        1333   39.95     0.32   F    0.00 0.14                                        1404   45.09     0.36   F    0.00 0.18                                        1451   52.14     0.41   F    0.00 0.23                                        1522   57.14     0.45   F    0.00 0.27                                        1553   62.31     0.49   F    0.00 0.32                                        1624   66.72     0.53   F    0.00 0.35                                        1654   70.33     0.56   F    0.00 0.38                                        1725   73.51     0.58   F    0.00 0.40                                        1755   75.74     0.60   F    0.00 0.42                                        1826 (dusk)                                                                          76.65     0.61   F    0.00 0.43                                        __________________________________________________________________________

I claim:
 1. A method for determining rate coefficient of smog formationin air, the method comprising:(a) adding excess nitric oxide to an airsample to provide an excess nitric oxide/air mixture; (b) permitting themixture to react for a first selected reaction period wherein excessnitric oxide in the mixture reacts with substantially all ozone in themixture; (c) determining a first nitric oxide concentration of themixture after the first selected reaction period; (d) illuminating themixture of (a) or the mixture after the first selected reaction periodfor a second selected reaction period under reference temperature andillumination conditions; (e) permitting the mixture, after illumination,to react for a third selected reaction period wherein excess nitricoxide in the mixture reacts with any ozone present in the mixture; (f)determining a second nitric oxide concentration of the mixture after thethird selected reaction period; and (g) determining the rate coefficientof smog formation from the first and second nitric oxide concentrations,the reference temperature and illumination conditions and the durationof the second selected reaction period.
 2. A method for determining rateof smog formation in air under selected temperature and illuminationconditions, which method comprises:(a) adding excess nitric oxide to anair sample to provide an excess nitric oxide/air mixture; (b) permittingthe mixture to react for a first selected reaction period wherein excessnitric oxide in the mixture reacts with substantially all ozone in themixture; (c) determining a first nitric oxide concentration of themixture after the first selected reaction period; (d) illuminating themixture of (a) or the mixture after the first selected reaction periodfor a second selected reaction period under selected temperature andillumination conditions; (e) permitting the mixture, after illumination,to react for a third selected reaction period wherein excess nitricoxide in the mixture reacts with any ozone present in the mixture; (f)determining a second nitric oxide concentration of the mixture after thethird selected reaction period; and (g) determining the rate of smogformation from the first and second nitric oxide concentrations and theduration of the second selected reaction period.